I mean it hasn't directly effected what I buy, but it has been kind of a hassle since certain games I own require PSN for DLC, like ME2 for the PS3. I ended up just starting ME2 anyways and just going with the default decisions, and I guess maybe I'll do a second playthrough with the choices I really want.
I ended up getting NBA Jam for the PS3 as well since I wanted a basketball game to play (even though I don't really know the full rules of basketball... but that makes Jam the perfect game for me, haha

). Probably helps that I don't really plan on playing that game online too much, so just screwing around with the CPU is plenty fun.
The biggest issue with PSN being down for me though has been the fact I own all my fighting games on it, and so I haven't been able to play those with friends in a while. I really wanted to play Arcana Heart 3 with a friend, which came out right before the PSN went down, and so I still haven't been able to play that.
I also promised to play Portal 2 co-op with one of my best friends but we both have to wait until the PSN is back to play it since neither of us were able to link the game to our Steam accounts before the PSN went down.
So I guess it is effecting what I'm playing and not playing more than what I'm buying.