Recently I used Console Debugger and find out maybe all of those World of Goo Online APIs. All World of Goo does is fetch a url and get the result.
Following are the APIs.

Don't open them with your browser casually because it WORKS!

Get Player Key: (click connect in the World of Goo Corporation)

https://worldofgoo.com/wogbuddy2.php?hwkey={hwkey}&name={name}&op=GetPlayerKey&version={version}

hwkey: Seems to be some kind of code for checking. Anyway mine is this one: 93540be1cc0a8c61e6ea0f0f3a4b9d47.
name: No doubt, it's your player name.
version: The version of your World of Goo. For example, mine is 1.40win (1%2e40win).

Result: A player id (described later), An online player key (also described later), your player name, and your country code (determined by your IP address).

Example

POST:
https://worldofgoo.com/wogbuddy2.php?hwkey=93540be1cc0a8c61e6ea0f0f3a4b9d47&name=Mygod%20Data%20Fetcher&op=GetPlayerKey&version=1%2e40win

Response:

<?xml version="1.0" encoding="UTF-8"?>
<WogResponse op="GetPlayerKey" result="OK" message="created player Mygod Data Fetcher id 7488097">
    <playerkey>df97bc13a9a8d0a02e1939055181f9dd</playerkey>
    <name>Mygod Data Fetcher</name>
    <countryCode>CN</countryCode>
</WogResponse>

Set level statistics: (submit: World of Goo LEADERBOARD of EXCELLENCE)

https://worldofgoo.com/wogbuddy2.php?balls={balls}&levelid={levelid}&moves={moves}&op=SetLevelStats&playerkey={playerkey}&time={time}&version={version}
balls: Goo balls collected in this level.
levelid: The id of your level, or the directory name of your level.
moves: Moves used in this level.
playerkey: Online player key. It is stored in your profile and get from the server by using the one above.
time: Seconds used in this level.

Result: Nothing useful, only a message: recorded levelstat for player {name}, levelid {levelid}

Example

POST:
https://worldofgoo.com/wogbuddy2.php?balls=4&levelid=GoingUp&moves=3&op=SetLevelStats&playerkey=a647df2dd93935fab47ee234693e7740&time=5&version=1%2e40win

Response:

<?xml version="1.0" encoding="UTF-8"?>
<WogResponse op="SetLevelStats" result="OK" message="recorded levelstat for player tmp, levelid GoingUp"/>

Submit your tower:

https://worldofgoo.com/wogbuddy2.php?ballCount={ballCount}&ballCountAttached={ballCountAttached}&height={height}&op=SetWogcStat&playerkey={playerkey}&version={version}

ballCount: Goo balls you have collected, for example 1300, but not 300 which is the upper limit of World of Goo Corporation.
ballCountAttached: Goo balls you have used to build a tower in World of Goo Corporation.
height: The height of your tower.

Result: Your rank!

Example

POST:
https://worldofgoo.com/wogbuddy2.php?ballCount=23&ballCountAttached=3&height=2%2e0&op=SetWogcStat&playerkey=a647df2dd93935fab47ee234693e7740&version=1%2e40win

Response:

<?xml version="1.0" encoding="UTF-8"?>
<WogResponse op="SetWogcStat" result="OK" message="">
    <rank>5519948</rank>
</WogResponse>

Get other players' statistics:

https://worldofgoo.com/wogbuddy2.php?height={height}&op=GetWogcStats&playerkey={playerkey}&version={version}

Result: Other players' statistics.
player_id: The id of the player. Maybe 6000000 means you are the 6000000th player in World of Goo!
player_name: The name of the player.
heightMax: The max height of the tower you have uploaded.
countryCode: Your country code.
timeCreated: The time of you click connect in the World of Goo Corporation. Time zone: -7:00
timeModified: The time of the tower was uploaded.

Example

POST:
https://worldofgoo.com/wogbuddy2.php?height=0&op=GetWogcStats&playerkey=a647df2dd93935fab47ee234693e7740&version=1%2e40win

Response:

<?xml version="1.0" encoding="UTF-8"?>
<WogResponse op="GetWogcStats" result="OK" message="">
    <HighTowerStats>
        <HighTowerStat player_id="7488208" player_name="dy" height="10.5" heightMax="10.5" ballCount="275" ballCountAttached="83" countryCode="CN" timeCreated="2012-08-21 20:35:43" timeModified="2012-08-21 21:25:18"/>
        <HighTowerStat player_id="7486684" player_name="L" height="12.8" heightMax="20.9" ballCount="718" ballCountAttached="153" countryCode="IR" timeCreated="2012-08-21 07:14:57" timeModified="2012-08-21 21:25:13"/>
        <HighTowerStat player_id="7328975" player_name="Surmak" height="15.2" heightMax="29.4" ballCount="1757" ballCountAttached="278" countryCode="US" timeCreated="2012-07-12 21:32:08" timeModified="2012-08-21 21:25:11"/>
        <HighTowerStat player_id="7177384" player_name="" height="6" heightMax="13.5" ballCount="375" ballCountAttached="107" countryCode="CN" timeCreated="2012-06-01 19:06:08" timeModified="2012-08-21 21:25:01"/>
        <HighTowerStat player_id="6150690" player_name="12" height="8.2" heightMax="12.4" ballCount="369" ballCountAttached="69" countryCode="RU" timeCreated="2011-10-04 21:05:56" timeModified="2012-08-21 21:24:46"/>
        <HighTowerStat player_id="7487539" player_name="santiago" height="12" heightMax="12" ballCount="183" ballCountAttached="60" countryCode="CO" timeCreated="2012-08-21 14:36:21" timeModified="2012-08-21 21:24:25"/>
        <HighTowerStat player_id="7488354" player_name="RK" height="6.4" heightMax="7.1" ballCount="74" ballCountAttached="23" countryCode="CN" timeCreated="2012-08-21 21:19:57" timeModified="2012-08-21 21:24:22"/>
        <HighTowerStat player_id="7488323" player_name="12" height="10.4" heightMax="10.4" ballCount="182" ballCountAttached="46" countryCode="RU" timeCreated="2012-08-21 21:10:43" timeModified="2012-08-21 21:24:20"/>
    </HighTowerStats>
</WogResponse>

P.S. It seems worldofgoo.com isn't stable so sometimes you will get a empty response.

EDIT: Just figured what hwkey is.