Quote from: btc123 on May 19, 2012, 01:17:53 AM

The balance in my wallet fluctuates up and down quite a bit. I backup my wallet maybe once every couple of weeks.
What would happen if my computer crashed and I restored a wallet that has more bitcoins in it than the wallet that I lost?

Would the system know which coins I no longer hold or would my transactions fail a lot?

It's a prudent practice always use new addresses and backup your wallet not every couple of weeks, but every 50 transactions or so (Keep your fuel tank at least half full).