If you go to my user page on Stack Overflow and you check it with the Google Toolbar, you can see it has no PageRank at all (this does happen for almost any user page, even people with much higher reputation, the only exceptions seem to be the users in page 1, and some other users they have PR).
My user page's Page Rank is not only zero, but not calculated at all. When PR is 0 or less than 1, but calculated the Google bar shows white, but when the PR is not even calculated like in my user page the Google bar shows in grey.
I further more discovered that my user page is NOT EVEN INDEXED on Google, simple test is searching on Google for the exact page url: "http://stackoverflow.com/users/260080/marco-demaio" and you will see no result.
The question is how can this be??? This is really weird to me because of the following reason:
If you search on Google for "Marco Demaio" on Stack Overflow only (you can do this by searching "site:stackoverflow.com Marco Demaio") the search result shows hundreds of 'asking/answering questions' pages where I was 'tagged'!!! Let's check one of these: the 1st one that appears now (shows one of the question I asked).
We can be sure this page is indexed in Google because comes out in a search. Moreover, its PR is calculated. It's probably nearly zero. Still, some PR flows there, the PR bar is not grey, but white:
The page shown above has got links to my own user page. I checked the source code of the page shown above and the links are not hidden or set with a rel="nofollow", moreover I can't see any meta character excluding the links on the page from being followed.
So what's happening? Why Google does not see my user page at all.
Did Stack Overflow do something to achieve this? If yes what did they do?
Any explanation really appreciates (as always).
P.S. obviously I checked also the code of my user page, but I could not find meta tags excluding Google search for the page.
P.S. 2 in a desperate adventure I also checked Stack Overflow's robots.txt but it does not seem to exclude user pages.
following up on some answers, I did some more research. Excluding for a while the PR problem (since PR is not science), and looking only at the user page on Stack Overflow NOT BEING INDEXED problem: pages do not seem to be indexed by Google because of the user reputation, this user for instance has got NOW 200 points less reputation than me and his page is indexed (while mine not). It does not seem even to be connected with months you have been on Stack Overflow, this user (almost my same reputation) has been there for 3 months only and his page is indexed (while mine not and I have been a user for 7 months).
UPDATE February/2011 As of today, the page got indexed by Google at least when you search for "site:stackoverflow.com Marco Demaio" it's the 1st page. The amazing thing is that it has still got NO PageRank at all: Google toolbar states loud and clear "No PageRank information available".