I have wonderful memories of PSO on the Dreamcast and Xbox. I've never put more time or passion into a game as I have into PSO. Since then I've tried every MMO under the sun: Everquest II, WoW, RF Online, and right now Anarchy Online, but PSO is still my favorite, probably because it's so simple and since you do the same levels over and over again, it gets to the point where you can just have conversations with people as you play (on Xbox with voice chat, anyway) without really thinking about what you're doing gameplay wise.
I love PSO, but I don't have the money for any kind of monthly service. And I didn't like the PSU beta too much, I'm not sure why...
(Speaking of which, you can still download the PSU beta on 360 and play for free, but I don't know where it cuts you off.)
If Blue Burst went the way of Guild Wars and had a one-time fee like the old PSO did, I'd jump on that like a beast.