In our own history, we were asked once to remove user profile from miniBB, because it was much more better indexed by one keyword, than owner's project itself (which was indexed by his nickname).
It is not a proof against indexing profiles, though. It only shows 1) how great and seo friendly minibb is 2) that users lack of knowledge on how to make his project better ranked in search engines.
So, in the next release, we will try to add "rel=nofollow" tag to all users profiles, and in user profile itself, there will be "nofollow" tags on each link you might see on the page.
I can see how useful that might be for some boards, yet if possible, I would like to have it optional (no matter what the default mode will be), or at least easily "hack-able".