I've had Xbox Live! for some time myself for the normal Xbox and the 360 as well.
I must admit that lag is less an issue there as it is on PSN, but like PARANOIA said it's free so how can we argue about that? :P
Also the games available on PS3 don't really stimulate me to play them online, i tried Tekken 5:DR a few times but the lag was horrible so i decided to not play anymore.
Maybe if some 2D Beat 'em ups were available on the PS3 i would start playing again, since i'm really into those.