Reading about the "change" addresses and doing "wallet.dat" backups, I keep reading that -by default- bitcoin-qt generates 100 keys and use them when you need a new address. My question is this: what happens after you use all 100 keys (for change, mainly). bitcoin-qt generates another block of 100 keys?. Only one?.
The information is critical for backup policy, and I can't find it online.
If you get a new 100 keys block, doing regular frequent backups is mostly fine, but if only a new key is generated, you should backup the wallet after any incoming or outgoing transaction...
Better yet, bitcoin-qt should have a permanent pool of 100 addresses, and add a new random address when you use one, in a FIFO style. That way you should be quite safe if you do less than 100 outgoing transactions between backups!.