Updated to release candidate 6:
https://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.4.1/test/
https://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.5.0/test/
Two changes were made between rc5 and 6:
1) When you encrypt your wallet for the first time, a new keypool is created before Bitcoin-Qt/bitcoind shuts down. This prevents losing bitcoins if you backed up your newly-encrypted wallet, received coins to new addresses, and then later restored from the backup.
There is still a potential problem when you upgrade a previously-encrypted wallet: in that case, the wallet file is rewritten on startup and will be left with an empty keypool (new keys cannot be written because in this case the code doesn't have your wallet passphrase). The release notes suggest backing up the re-encrypted wallet after generating a new address.
2) Be less aggressive about deleting the database/log.* file(s) on shutdown -- with rc6, they are only deleted if the wallet is successfully encrypted/re-encrypted (to make sure unencrypted private keys are not left in them).
Please report only show-stopper bugs in this thread-- normal bug reports or feature suggestions should go into the github issue tracker:
https://github.com/bitcoin/bitcoin/issues
Please DO add to this thread if you've done some testing, giving what you tested (0.4.1? 0.5.0 ? win32 exe ? zip ? linux ?), what operating system you tested on, and if you were testing a fresh install or upgrading (and if upgrading, was your wallet encrypted before?).