PSN has made strides to be a much better service now.
By the way, aren't they gonna be called SEN?
Nope, the PSN was never going to be called SEN. It is, however, a part of SEN. SEN is Sony Entertainment Network which covers multiple Sony projects including the PSN. Basically SEN is just a blanket name Sony decided to use.
As for Live being worth the purchase price? In my opinion, no. My main console is the PlayStation 3 so I use my 360 just for it's exclusive titles (mainly Forza.) So naturally I don't play as much online with my 360 as I do with my PS3 so it's a little hard for me to justify the price. Also, I am extremely annoyed that Microsoft forces a Gold membership if you want to use their Netflix app, meaning you have to pay to use something you already pay to use.
I'll also throw my opinion in on the subject as to which one is "better." To me PlayStation Network wins bar none. Not because it has better features or anything like that, but simply it performs exactly like Live, but it's free. I've played multiple games on each system and I've never had a problem with either one. Both have experienced nearly the same amount of lag, both download games and demos at comparable rates, and while Live may have some extra features I don't use any of them so they aren't exactly going to be a selling point to me. I've heard time and time again that Live is a better service, games are laggy on the PS3, downloads suck on the PS3 or whatever else, but I'll just say that isn't my experience or anyone else I know with a PS3. If you are experiencing those issues I'd look into your own internet connection first.
For a shorter answer: If the 360 is your main console a Live subscription could easily be justified. If you're like me and it's a secondary console not used often a Live account may be a waste of money.
Parker