We’‘ve been using Spark in a Windows/Mac/Linux environment for a few weeks, and thought I would report a couple of bugs that I havn’'t seen mentioned elsewhere:
Windows - If you recieve a Spark message whilst playing a video in Windows Media Player 10, the colours get all messed up and the video starts looping very rapidly. You have to stop and start the playback to fix it.
Mac/Linux - conference invites are never received.
And my all time big bug that I have mentioned before (!