1st of all congrats for PR4 2nd thing is its good that you maintain PR4 . i mean getting rich is diff. thing . maintaining ur richness is other thing . if u not grow more at least u hold the same position.
And watch your friends stop linking to you for acting like a twat. BTW the nofollow tag will not pass additional PR to other pages.
Getting a .edu or .gov link is very hard. I tried hard and finally got one after much effort. so its better to try other methods.