TimThumb is hosted on http://code.google.com/p/timthumb/, more documentation on the website of the author BinaryMoon.
I had problem with TimThumb, first off all with my multisite but i found a nice fix written by my Dutch colleagues on http://www.letuslook.nl/how-to-make-timthumb-work-in-wordpress-multisite/.
Then TimThumb was scaling up my small images!
I searched for a couple of hours for a fix but no good results. The only interesting result I found was about the same issue I had (over here). In the issue they refered to an older version of TimThumb which is located here (#69). Well with that version i was capable of fixing my upscaling problem.