Most of you know Netflix's streaming service is unavailable to PowerPC users as it uses Silverlight, but there are alternatives that are flash-based like Hulu, although Hulu users have to use the Flash hack to fool your browser it's using Flash 11. But I wanted to talk about a new kid on the block, Amazon Instant Video.
Like Hulu, it uses Flash, but it still recognizes Flash 10.1. The bad news is that it's Flash, so performance isn't that great, but they have a good selection of videos. The prices for one-time rentals are a bit high in my opinion, but Amazon Prime members get free unlimited streaming to a separate library of movies and TV shows that don't include new releases.
The fastest G4 I tried this on was a 1.5 GHz AlBook and it was watchable, though there was noticeable frame-skipping. Performance and picture quality were roughly on par with Hulu. So if you have a fast G4 or G5 and were considering signing up to Amazon Prime for its free shipping and Kindle perks, the free streaming might be something to consider.
Though they could always drop Flash and switch to Silverlight and brag on their homepage that they support both Windows and Mac!