This works in Firefox, Chrome and Safari. You seem to have to sign up in every browser...
+1 doesn't seem to work in IE7 anyway. IE8 does an (i)frame detect and doesn't show the +1 buttons if it is in a frame. You can make it work for this example by opening this, refreshing so the buttons appear then hitting back. Any ideas to fix? Twitter me!
Disclaimer: This was just a bit of fun / proof of concept, please don't use this to embed +1 buttons on your sites. Google will provide this feature soon! Certainly don't use it to scam people into +1'ing some other site they don't realise they're voting for.