For info : the bug has been noticed on a computer featuring Windows XP pro sp2 and a nVidia 8600 GT 256 Mb graphic card.

It displays parasites on the screen (short horizontal lines appearing a disappearing quickly during the game).

The bug can appear after 1 or 2 minutes and continues under Windows, even if you close the game. You may have to restart the system to get rid of these lines.

Images:
http://img380.imageshack.us/img380/5296/alim1889tf1.jpg
http://img116.imageshack.us/img116/9598/alim1885tz4.jpg
http://img210.imageshack.us/img210/9903/alim1886tu7.jpg

ANSWER :
To solve this problem, modify the "C:\Program Files\WorldOfGoo\properties\config.txt" file. In fact you just have to change the refreshrate value from 60 to 50.