I've been a member pretty much since I got my PS3, I find generally the good points outweigh the bad ones. If you break down the "cost" per game it's very very cheap, particularly when titles such as Red Dead Redemption appear. There's actually less of the PS1/PS2 games now since they revamped it all recently, but you still get Minis/Indies, which I like but they aren't everyone's cuppa i guess.
The down side for me is that of course there will sometimes be games you already have, but personally I don't buy a lot of new titles anyway, i'm very selective so PS+ kinda covers off games I perhaps wouldn't ordinarily try, with some nice surprises.
That said, there does seem to be a focus on first and third person shooters and sci-fi-themed titles, most of which are good but honestly not "great". I think they should shake up the variety a little, for example they recently had Double Dragon Neon and Scott Pilgrim but really SP is just a rehash of games like DD with modern, cartoony characters. I tried one after the other and they were fun but very similar.
Another thing that bugs me a little is the amount of errors they seem to make, for example where they forget to provide an unlock or make it clear how to find it, so you think you are stuck with the trial version. Other titles they forget to mark as free, for example I realised I hadn't checked for new titles recently so went to the PS Store and saw they were giving away Crysis 2, but it was full price. They took it down so I thought they were fixing it but no, it was gone. It was only up for a month whereas Motorstorm 2 (whatever it's called) seems to have been on there about a year. Odd.
Also i'm not sure what will happen in the future when the PS4 comes out. Will we have to remain members of PS+ to retain our "free" games or will they eventually grant an unlimited licence? There's a chance I might not want a PS4 so would suck to be tied in and not get any more games.
OK that's a few negatives but believe it or not, I think they are still outweighed by the positives
