I've had the same problem and I can provide some additional details.
1. The problem is definitely with Ubuntu, I've tried on a different OS and was successful
2. I've added rules to Firestarter to allow access from the PS3 and then tried turning the firewall off completely and both were unsuccessful.
3. I can ping the PS3 from Ubuntu.
My guess is that, as stated above, the problem is somewhere in the networking of Ubuntu. I hope that helps.