I have had the 0.8.0-qt client crash on me twice in the past couple of weeks with the cryptic message "Failed to write block." I'm on Mac OS X and have plenty of disk space. I'm upgrading to 0.8.1 as we speak, but the OP spoke of this happening with 0.8.1, so I doubt it will fix the problem.
you can always delete everything in the bitcoin data directory except for wallet.dat (and maybe bitcoin.conf if you have it), and allow the client to redownload from scratch.
You aren't offline when building the blockchain and I ask as I had similar problem which seemed to be solved when I changed from chrome. Every time I try using chrome the wallet crashes.
lolwut