With a little help from xda-developers, Ausdroid has managed to get Google Wallet working on a Nexus S. Sure, you can only spend $US10, but it's your first chance to try the service out before it arrives locally... which I'll readily admit could be never. So perhaps your only chance.
Getting Google Wallet to work is not straightforward and even if you do manage it, there are a few caveats. As previously mentioned, you'll only be able to spend $US10, provided as pre-paid credit. There's no way to top up your account, so spend your rich bounty wisely. You also at one point had to completely wipe and reinstall your ROM, though this is no longer necessary. If you have root access, then it's a matter of uploading a file and using ClockworkMod Recovery.
According to Ausdroid, the pre-paid credit is the primary reason the hack works at all, so if for some reason this offer is discontinued, then I imagine this would stop working, too. Well, you wouldn't be able to buy anything, which kind of defeats the purpose.