This is the thread to end all threads (ok, half of them) at 2D Boy's forum.
Some of the questions are already in the goofans.com FAQ, some aren't.
@david, you could make another page for this or add them in the existing ones if you like.

Word of Goo Noob FAQ

Summary

Official Level Editor? - Nope. download zark92's WOGedit
World of Goo DS? (Xbox Live, PSN, or other platforms)? - Nope, nothing planned.
World of Goo 2? - Not likely to happen.
2D Boy's Next Game? - will be something else.
The Moon Chapter? - was canceled.
300 Goo Ball Limit? - Right, you can't get more Balls for tower building!

The real thing starts here:

Official Level Editor?

TR - I know the community has started working on a level editor, is this something you plan on doing too?

Ron: We’ll do whatever we can to support the modding community, but we’re not planning on making a level editor ourselves.

Kyle: The community are amazing. They also translated the game into a bunch of languages, including Spanish, French, German, Italian, and Dutch. We ended up using the community translations for our brand new European releases of the game. They were able to maintain the humor and spirit of the game. I just hope nothing naughty snuck in.
(24 December 2008)
http://thereticule.com/2008/12/2d-boy-interview-part-one/

Kyle: One thing we're doing is offering support to make the whole game much more moddable. We're constantly surprised at the ingenuity of some of the people on our forum. Currently there's a level editor in progress, and another tool for editing parameters in the game, and a quickly growing open translation project to make the game work in as many languages as possible.
(12 November 2008)
http://nintendo.joystiq.com/2008/11/12/wii-fanboy-interviews-2d-boy-worl...

World of Goo DS (Xbox Live, PSN, or other platforms)?

If World of Goo becomes a big success on WiiWare, can you see it making its way to Xbox Live Arcade or PSN? How about a DS game?

Ron: XBLA and PSN will probably not happen, we just don't think the controls would feel right. Mouse is great and so is the Wii remote.
The DS would be a good platform for the game from a controls standpoint but the processor is not nearly strong enough for the physics simulation. We might be able to do a simplified version of the game, but we have no plans for that right now.
(12 November 2008)
http://nintendo.joystiq.com/2008/11/12/wii-fanboy-interviews-2d-boy-worl...

Why was World of Goo released only on WiiWare, and not Live or PSN?

Ron: The Wii remote was the only controller other than the mouse that made sense for this game. If we tried to make the game use a dual-shock style controller players would end up feeling like they're in a straight jacket.
(4 November 2008)
http://www.gamecritics.com/brad-gallaway/interview-with-2d-boy

World of Goo 2?

Can you see yourself making a sequel (or, better yet, bite-sized DLC add-on packs)? Or are you looking to move on to a different project next? What's the next step for 2D Boy?

Ron: No! No sequel! The only sequel to meet the expectations created by the original is The Empire Strikes Back, and even then, it was just because George Lucas didn't direct it. Also, we've eaten enough goo to last a life time and we're ready to do something else.

Kyle: One thing we're doing is offering support to make the whole game much more moddable. We're constantly surprised at the ingenuity of some of the people on our forum. Currently there's a level editor in progress, and another tool for editing parameters in the game, and a quickly growing open translation project to make the game work in as many languages as possible.
(12 November 2008)
http://nintendo.joystiq.com/2008/11/12/wii-fanboy-interviews-2d-boy-worl...

2D Boy's Next Game

Currently, World of Goo is holding strong at a score of 96 on MetaCritic, putting it alongside things like the Orange Box, BioShock, Super Mario Galaxy, and Resident Evil 4. That's some great company to be in. Now that the bar has been set so high, what are you working on now and what are your plans for the future? Do you feel any pressure to produce something as successful as Goo?

Ron: Our next game is going to be called "The Sophomore Effect: An Intentionally Mediocre Game". We have to lower expectations for our third game because there's no way we can top World of Goo.

Kyle: We'll see about that! In the meantime, we're incredibly grateful about our review scores. Of course, I have a feeling our sales are orders of magnitude less than Mario Galaxy!
(4 November 2008)
http://www.gamecritics.com/brad-gallaway/interview-with-2d-boy

Eurogamer: When Jon Blyth reviewed the PC version on Eurogamer, he said that he feared for you both having to follow it up. Do you feel that way at all?

Kyle Gabler: Yeah we don't want to make a Temple of Doom. But the next game will be a dumb arena shooter.

Ron Carmel: Hey, how did you know about my idea? I was going to tell you about it tomorrow.

Eurogamer: So apart from the arena shooter, are you working on anything now?

Kyle Gabler: The next step is to prototype a bunch of new ideas. One week each.

Ron Carmel: We have a bunch of ideas laying around, none of which is one of those "oh, that's a game" kind of ideas.

Kyle Gabler: Yeah, the plan is to make a bunch of stuff, and see what sticks.
(15 January 2009)
http://www.eurogamer.net/articles/2d-boys-ron-carmel-and-kyle-gabler-int...

The Moon Chapter

TR - You have made some mention to a couple of people regarding the mysterious 6th “Moon” Chapter; will this ever be released and what was it all about?

Ron: Originally, there was a plan to release World of Goo as a retail game for both Wii and PC in Europe, and to support the higher price needed for a retail release we were going to add a 6th chapter, called “The Moon”. There was an outcry about the price difference and the release schedule from European gamers and we decided to change course by releasing the game sooner, at a lower price, and without the 6th chapter.

Kyle: The Moon was a prequel to World of Goo, taking place “one year ago” when World of Goo Corporation was a brand new Web 2.0 startup company, and they decided to monetize the Moon by making it ad-supported with community features. Eventually they detonate the moon, and replace it with M.O.O.N. 2.0, a giant ball of homogenized glowing/flickering Goo Balls, to create a giant hi-definition LCD panel in the sky for displaying important animated marketing messages to the World of Goo down below. The plot is told through a love story, involving “The Architect” who changes jobs at the end, and becomes one of the characters we meet in World of Goo.
(24 December 2008)
http://thereticule.com/2008/12/2d-boy-interview-part-one/

300 Goo Ball Limit

Finally, is there an absolute limit as to how tall the towers in the World of Goo Corporation can go?

Ron: There can be no more than 300 Goo Balls in the Corporation. Even with the greatest of skill, a tower can only be so high. But the World of Goo, like every other computer system, has rules. Some of them can be bent, others... can be broken. Please don't mess up the leaderboards, Neo.

Kyle: World of Goo Corporation Executives have stated that World of Goo Corporation is infinite in all directions, and are enthusiastic to maintain that there is no vertical limit to our own Imagination(tm), provided additional Imagination Points(tm) are purchased at authorized Imagination Vending Dispenser Units(tm).
(4 November 2008)
http://www.gamecritics.com/brad-gallaway/interview-with-2d-boy