It's definitely worth the dosh if you don't buy a lot of games. Unfortunately I've now found that most of the games offered are things I've already bought on PC for bugger all anyway. The handful of PS3 exclusives have been things I've already played too.
I have saved a bit of dosh from the discounts though, so between that and a few "free" games I haven't already played I got my moneys worth. I'll get a Vita eventually so will be better value then.