I have stumbled to this topic while searching how to change the time of activation link before it expires.
So, @kriskl how much time it takes before activation link expires when registering to your site?
I have similar problem. The default time of 2 hours looks like very insufficient for users. We have almost no spam registrations and still there are many abandoned registrations.
On the net there is no easily reachable info how to change this configuration. I have posted two threads on WP.com, still no news. Hope some of you people can help or give an idea where is that php that sets the time period.