I've tried a few times and couldn't get this to work. First time, I just put the bootstrap.dat file there and tried to run it against my current blocks. It didn't like that and got stuck.

The next time, I deleted all my block data and tried it again. This time it got stuck at block 211551 (iirc) and wouldn't load any block after that. Looking at the debug.log, I see that my peers are trying to give me blocks higher than that but my client keeps rejecting them for some reason.

The third time, I tried the same thing again. This time, when it got to block 155088, it gave me a database corrupt message and the client quit. Restarting the client does the same thing:
init message: Importing blocks from block database...
LevelDB read failure: Corruption: block checksum mismatch

I'm running this on a Mac if that makes a difference. Seems like 0.8 is buggy.