0
Is %APPDATA%\Roaming\Bitcoin\wallet.dat the only file I need to backup my wallet?
I've heard about backing up every ~50-100 transactions is this correct? I thought that with the wallet.dat file, I have my private key, which is all that I need to restore my bitcoins.
0
Yes. The wallet.dat file is all you need to be able to keep your coins backed up. You'll also obviously need your password if you've encrypted your wallet.
However, backing up the entire folder may be advisable if you're on a slow internet connection. The blockchain is getting rather sizable and can take a significant amount of time to redownload from scratch. I recently needed to do that and it took almost 2 full days.
1Note: Unless you spend all "input", you will get some bitcoins 'back'. Bitcoin-qt will automatic assign a new bitcoin address to the "charge" (for security and privacy reasons). Your wallet.dat will contain a "key pool" of 100 new bitcoin addresses, but when theses are spend, then bitcoin-qt will generate a new addresses. So backup every 100 transfers, or change the default key pool size by running bitcoin-qt once with the parameter:
(where n = how many keys to pre-generate, eg 1000). – Nicolai – 2013-03-12T15:43:09.590