I'm running it 1.1.4 on my G5 PPC and my Intel Macbook, both running 10.5.8, without any problems at all. I use video daily, editing it, watching it, and converting it, and have never had a problem with Perian. I couldn't do most of the things do very easily or quickly without Perian. I would say it primarily gets its biggest work out with the Nice Player, my preferred player because its slick and has a play list ;)

If you're running Snowleopard and experiencing issues, head over to the Perian forum http://forums.cocoaforge.com/viewforum.php?f=25 and see what people are talking about and what the discussion is... the developers and people who know their video stuff often contribute to the discussions so the forum is very valuable.