In the Steam version, there are 8 achievements that can be unlocked:

Executive Producer of Goo Product

All Levels Complete

Subversive Traveler

there is a secret (spoiler)

Engineer of Goo I

All OCD Flags in Chapter 1

Engineer of Goo II

All OCD Flags in Chapter 2

Engineer of Goo III

All OCD Flags in Chapter 3

Engineer of Goo IV

All OCD Flags in Chapter 4

Engineer of Goo V

All OCD Flags in Chapter 5

The Architect of Goo

All OCD Flags

Completing these achievements gives you nothing except bragging rights on the Steam website .

In early versions of World of Goo, once you've completed MOM's Computer, you can't replay it. Therefore you cannot try again for the OCD.

Simply patch World of Goo to the latest version and you will be able to replay this level.

Unfortunately it is not possible to upgrade the Wii version.

You obtain the whistle after completing the level "Leap Hole" in Chapter 2. Once you have it, you can use it any level (including earlier levels if you go back to them).

To use the whistle simply hold down the left mouse button anywhere except on top of a ball. Nearby unattached Goo Balls on structures will begin to move faster, and will adjust their movement to generally move closer to where you're whistling.

Windows/Linux: Simply press ALT+ENTER once the game is loaded, and it will toggle between window or full-screen mode.

Mac OS X: Press Command+F.

Short answer: you can't.

Everyone is limited to 300 balls for their tower. Even though their cloud may show more balls, that's the total number of balls they have collected. They're still limited to 300 balls in their tower.

Long answer: The limit had to be the same for everyone worldwide to make the leaderboards fair. 2dboy chose 300 as the limit, as more balls caused people's computers to slow down too much.

Rant: The clouds in the corporation show their total balls (even though they're really limited to 300) which causes this question to come up again and again.

Cheater's answer: you can if you hack the .exe but I strongly disapprove of this and it is liable to slow your computer down to a crawl anyway. Instead why not play the sandbox level?