I run Bitcoin-qt on multiple computers, and sometimes one machine will go a few days before being turned on.  One of the frustrating things about using Bitcoin-qt is that, after waiting what feels like 5-10 minutes for the program to completely verify the block chain, you may have to wait another 20 minutes for the rest of the blockchain to download and verify.  I believe some time could be saved, but one of the devs will have to confirm.

Probably on every machine, the bottleneck during startup is the hard disk.  The CPU is relatively idle, and the network isn't being used at all.  I would guess that 99.9% of the time, it would be a safe assumption that the stored blockchain and database have not been corrupted.  Would it be possible to look at the last block stored locally, and begin "prefetching" the rest of the blockchain from any nodes the client can see?  The local blockchain would of course still be verified as usual, but you'd save a few minutes by having the new data already downloaded by the time the rest of the chain is verified.  The new data would just be cached in RAM (or disk if there was enough of it) until the verification process caught up.

Thoughts?  Possible?