I am having the same problem. I connect and start running around, and within 30 seconds I get the "Server is not responding, try back in 5 minutes" message. However, my situation is even stranger. I have been playing PS over the last week religiously. I was even playing it a few hours before I left for work. But when I came home, I couldn't connect (or stay connected). That was almost 4 hours ago now. I have been constantly checking the server status, and it claims to running fine with 80+ users.
The only thing I changed between the many many hours it worked fine and now was adjusting some settings in pssetup. Specifically, I tried using a different resolution and adjusted downwards the quality / speed options. Even though I changed them back, nothing. Could they have altered the config file in such a way as to not be fixed when returning to default settings?
Just in case: I am running a powerbook g4 (1.25) with 768 ram, ati radeon 9600 (64MB), and OS X 10.4.8.