I bought Journey during a sale a while back. At under $4 (with PS+), why not?
I've actually bought a few games off PSN here and there, most recently Okami HD and D&D: Chronicles of Mystara.
(Normally, I'd buy the latter on PC, and I probably will when the inevitable Steam sale hits, but a game like that just has to be played in the university game room, with people on couches next to you. I don't trust my little HP 2730p with its godawful Intel graphics to be capable of running any PC game these days.)