Well, the PR matters if you want your twitter page to rank, because PageRank is one of more than 200 different signals that we use in our rankings. So, if you want to do a search like Matt Cutts and have twitter.com/mattcutts show up then the PageRank does matter for that Twitter profile page. It generally doesn’t matter for the ongoing links on that page because those tend to be no-followed.
But bear in mind that it can be that the guy who only have 50 followers and 100 tweets might have still gotten someone really important or authoritative to link to him. So, that might be why he or she has a PageRank of four. As far as why a more meaningful, more meaningful profile doesn’t have PageRank, sometimes they can be that you don’t have anybody linking to you or very few people linking to you. It could also be that maybe you do have some important people linking to you, maybe there’s a newspaper article. But we only compute PageRank in and we compute PageRank continuously; but we only push out new values of PageRank to the tool bar every three or four months or so. So it could be that you got a good link a month or two ago, but you’ll still have to wait another month or two before that PageRank shows up on your Twitter profile page.
I would be thinking about, okay, how do I engage users? How do I get users to comment and reply and go to the places that I link to and things like that because talking to people is the primary value of Twitter; sharing good links, conversing back and forth rather than PageRank or rankings that you’ll get as a result.
by Matt Cutts - Google's Head of Search Quality Team