I've read on few places that Songbird is no good with more than some thousands of library items because it starts getting quite slow.

Well, in my case (which is a clean install) I've imported 17k items (which I know is not that much) and instead of becoming just too slow it frequently gets to not responding for several minutes until getting back to its senses again. That's for whichever random operation such as deleting 1 item from library.

I've also read on few more places that gives very little hope on fixing this issue, but I wonder...

Is there any way to tweak it and make it work as fast as expected? Am I missing something or is the software just not intended for libraries with more than 10 thousand thingies?