Installing bitcoind from github, I forgot to pass "git checkout v0.8.6" (current version at time of writing), and of course, go the following error in getinfo.
"This is a pre-release test build - use at your own risk - do not use for mining or merchant applications"
This got me thinking, what kinds of unexpected problems which could happen?
It might contain security vulnerabilities (which could potentially expose your private key), but that's extremely unlikely. Something more plausible (but still unlikely) is corrupting your wallet.dat, so be sure to back it up before upgrading.
As a normal user, the test build ought to be safe for most purposes. The main risk, I guess, is for people operating exchanges, mining pools, etc., where you can't afford to go down in the middle of operation. The test build is more likely to crash (or fail to work in some way) rather than be insecure.
Test builds are more likely to have bugs since they're less thoroughly tested. Bugs could range anywhere from wallet corruption to crashes to accidental spending.
In general, it should be pretty safe, but there's no guarantees of stability.
