cant say ive had an issue like that.
When switching consoles from my old YLOD model to my new one, it was a simple transfer (after getting the old one running again)
otherwise the only time ive had an issue of it dropping out is on my brothers PS3, when we installed GT5 we also had 4 other comps interneting at the same time and it had a little error in the last 3% of the updates (all of them), but it had only forgotten about 300mb the next time round. so no big issue