Since I've first heard of bitcoin I've been facinated by the idea and the project. One of the most appealing qualities is it's potential both the long and short term. If all it is ever going to be is a way for hackers to tip their favorite cartoonist, that's great. If it turns out to be a large scale tool to protect the privacy of individuals against totalitarian governments and other large organizations, it is great. If it turns out to be a workaround to cope with central banks massively devaluing their currency, that would be wonderful.
# Malware unrelated to bitcoin could extract the relevant contents of wallet.dat and steal the money. Protecting the wallet with a good symmetric crypto would manage some of this risk, but I think that it would be advisable to have wallets with nontrivial amounts of bitcoins associated with them on removable media such as USB drives.
/noa
Securing the wallets on local machine ... yep, it needs some serious looking at ... 'deleted' copies of wallets and fragments are probably being left lying around all over the place. It will take some really tight low-level file/memory management to make it bullet-proof, probably be quite high commercial demand for some top-shelf wallet management s/ware also.