I've enabled the google code verification. Here is my feedback:
1) When accessing the forum for the first time with a deep link (e.g. going to a specific forum post) that URL is not used for redirecting after the code was successfully validated. Please, use that url. At the moment I have to click, enter the code, get back and click the URL again. Its cumbersome.
2) When using a mobile phone, the forum pages are optimized for mobile use. For entering the verification code I have to switch to desktop view, and after code verification back again. Its cumbersome, too.
3) I personally would prefer if the redirection would get you immediately to the targeted URL - without any delay (not showing "code accepted" or whatever it says). If the code is wrong, such a display and delay is fine. But not if is ok.
4) Google presents the codes in packets of 3 digits. If you enter them as shown (with a blank in-between) you do not accept the code. That can be confusing to new users. Please, accept (remove internally) blanks from the input.
5) If you entered an incorrect code there is no (obvious) way to get back to the input field again. Here I would prefer that the same page (code entry) would be displayed with the error message below, so one could try again.