I don't think so, since I was just racing online with a few people I normally race with a couple of minutes ago. I think the GT5 servers are just having a little bit of trouble, not completely down.
Today, just now. Try rebooting the game, usually works for me. But I can tell you one thing; it can't be maintenance because they would have told us about it long before it actually started.
I haded issues earlier today while competing in a race online that later got me disconnected from the room the race was held in. After I saw the disconnected notice, my PSN account automatically sign me out. After signing back in I return to the room, and guess what. I get disconnected, and auto sign out again. I don't think it was the GT5 severs, but I think it was probaly the PSN fault because I never have this problem in the past where I just get disconnected, and remain online.