Am running 8.1.5 on OS X 10.6.4 (on a 2.2GHz MBP w/2 GB RAM), with MOTU Ultralite with 512 sample buffer, Delay Compensation off. TC Electronic M30 Reverb on one return track, Live Ping Pong delay on the other return track.
I have a project which has about 8 instances of KontaktPlayer2 (using Garritan Personal Orchestra samples) and pretty much every time I start a new clip I get a very audible drop out of the whole audio. But the daft thing is, it's not consistent - I just tested it again while writing this post and now it's fine.

CPU sits at 25% when no clips are playing, rising to 30% when all 9 tracks are playing (8 GPO, 1 external synth).
Live 8.1.3 seems to be the same; can't test Live 7 or 6 due to file format change.
So, is it a Live bug? Or is my laptop just underpowered?