For "preventative" measures, please do the following:
1. Clear your system cache. It's in your Network Options. No evidence that this helps, but it has been known to improve loading times in the past. If your PS3 talks to PDs servers, clear your system cache daily.
2. Disable custom soundtracks. Kaz mentioned this in a tweet a few weeks ago. Again, if your PS3 talks to PD servers (online races, Seasonal events, Remote Racing, item gifting- even the free paints and cards, etc.), you'd probably be better off listening to the car anyway. Most have reported a noticable improvement with Seasonals after doing this simple step.
3. Reset your internet connection before playing. See that power cord on the back of your modem? Yank it, then replace it BEFORE you power up your PS3 and access the network, let alone play GT5.
4. Pray to deity of choice. Might seem blasphemous, but who else are you going to call? (Ghostbusters is too obvious) Maybe YOU will be the lucky one Jesus/Mohammed/Allah/Xenu/Santa/Tooth Fairy will answer, and maybe they'll grant your one wish to fix your games and PS3. Probably not, though.
If all that fails, proceed to Sony customer support. They're about as useful as #4 anyway.
Good luck