I think you guys are missing the point. I'm not worried about my coins. I'm worried about the future of the bitcoin if someone were to launch that attack on the bitcoin network. If all wallet addresses were allocated, what measures are in place to reclaim empty/unused wallets?
Wallet addresses are NOT ALLOCATED.
Exactly. But in more detail: If you generate a wallet you are basically generating a (bunch of) key pair(s): a public one (basically this is the receive address) and a private one (which can send BTC that were received by its corresponding public key earlier). No one notices when you do this on your computer.
So, you can generate lots of addresses, but you can't do anything with them (do transactions that clog the network, so someone
does notice): unless you have some huge amount of BTC lying around you can send send them some fractional bitcoin. *
If someone else generates an address that is already generated in your astronomical pool, he can just use it. (And you can drain his funds, but this is astronomically difficult, as some else said before)**
* = spamming attack
** = generating lots of addresses: Collision attack
See
https://en.bitcoin.it/wiki/Weaknesses, it has lots of information and of course it explains it more elaborately than I do
