I didn't do too much of a stresstest yet; tried requesting a few hundred pages in relatively short time and that went well. But the number of daily visitors we have on that website outperform my stresstest by far, so I'd have to find an app or so that can do really good stresstesting (would be glad to hear how others perform stresstests)
I don't call any .Dispose() but found out that there's one class in my code that uses a separate Connection String which I didn't adjust (stupid, I should've built this into the web.config or something like that, will do that as soon as I solved this problem)
Finally, in another forum, someone told me that DataAdapters are meant to keep the connection open and I'd rather use DataReaders for such functions; see
http://forums.aspfree.com/showthread.php?t=46151
Does That Make Sense?