SVN rev 163 (ver 0.3.13.3) has the key pool feature. Pre-generated new keys are aged in a queue before use, so that backups of wallet.dat hold keys you'll use in the future. For now I made the default pool size 100. It can be configured with -keypool=. Be aware, it takes a little time to increase the pool size, so don't go crazy with it. Disk space is about 1K per key. I have not addressed the recovery side of this yet. If you actually did restore an old wallet.dat, I think you may have to delete blk*.dat to rediscover your own transactions during the redownload. I've only tested this moderately. You might not want to use this for a website server until it's had some more testing.
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