I'll blame the kids then...

Fixed it!

So, picture numerous cycles of...

• Clear system cache.
• Restore save game from spare drive.
• Format and install.
• Kneeling in front of the PS3 and crying.

And now I've fixed it. Here's the clue:

The final analysis goes something like this...

1. Random slowness and crashing in GT5.
2. Other games OK.
3. Demo won't play (the thing at the start).
4. Options are slow.
5. Worst, online lobby seems to crash out all the time, I just can't start a race online.
6. Even pressing the PS button to get the XMB up seems to stall everything.

So I checked everything I could, it seemed to be related to network stuff, but how, I even have a fast connection of sorts (7Mbps download in PS3 test FFS).

So what's going on. Forums don't really help, but then I find 'the' thread, try these things it says:

1. Clear System Cache in game (check, done that).
2. Clear Internet browsing history (ooo, new).
3. Synchronise Trophies in the XMB (check, done that).
4. Check the disk for finger prints (haha, yeah, whatever).

But then (and really there's no suspense to this is there) I check the disk. Here's clue number two, in conjunction with the one above:

Gosh, I didn't know finger prints came in 3D. I should have taken a picture of it. Honestly, I could have got a rag, wiped it (I did) and the results used to grease every moving part on a freight train. 

Anyway, humble pie fried in fat and eaten, I've put the disk back in, done the 'other' options above and all good. In fact, better than good - my game loads better than it has for a long time!

Oh yes.

And let that be a lesson to you all.