Update: I added a short video review of streaming on the PS3.
The Netflix streaming discs arrived today for the first 100,000 customers that requested it (get yours at http://www.netflix.com/ps3), and I spent a bit of time playing with the disc. Until they release an update sometime next year, you'll have to put the disc in every time you wan to watch streaming movies. The envelope even has a reminder: "Do not return disc to Netflix."
The PS3 streaming disc loads quickly, and the Netflix user interface is very similar to most Netflix-ready devices, with tabs across the top for Instant Queue, Recently Watched, New Arrivals, genres, Movies You'll Love, and even Netflix's Taste Preferences like "Feel-good Underdog Movies." The Xbox interface is a step ahead, with the movie sharing and a more advanced user interface, so it'll be interesting to see how fast Sony catches up (or passes them, given the rivalry).
The video quality is on par with other streaming devices, and the PS3 supports HD streaming from Netflix (the title with have a HD icon). If you're having trouble with HD streaming, NetflixHelps on Twitter says to make sure that display is set to 720p in the PS3 settings.
Here's a quick video review of streaming on the PS3:
Do you have the PS3 streaming disc? What do you think of Netflix streaming on the PS3?