Sometimes (I think it's only happened with Absynth) notes start to hang as if the note-release isn't detected. I've never experienced it during rendering - only during live playback.
It sounds like some notes doesn't get released and just keep playing.
Again it has only happened with Absynth but the only other VSTi I use is Battery 2, and it wouldn't really show if the sampler notes stayed on.
I'm on a 2.3ghz 1gb. ram machine with a Maya44 usb and a Korg MicroKONTROL. Works like a charm
If you need more information you can mail me.
Thanks for great software,
Taiis