Personally, I find wikis really useful for rounding out the character and the world they are in. Obviously, if a game's wiki or somebody's page asserts that information on it is strictly OOC, I don't use it. Nor do I ever use information regarding supernatural stuff/powers/etc unless I've seen those or had them described to me, ICly.
But, that having been said, wikis are basically a really good organic substitute for 'common knowledge' and office/school gossip. In the real world, we find out all sorts of things about people. Who has a reputation for being popular? Who is kinda bitchy? That quirky guy down in accounting? Total Jesus freak. The IT manager? Dude is a leather daddy on his off time!
And the same goes for neighborhoods, businesses, etc. As a substitute for background information immersion that we all get, wikis work fine. (Though I'd encourage people to lie on them about minor things, because office gossip often gets it wrong.)
The problem with an OOC masq taken to the extreme, banning personal pages, is that you raise the bar for engagement with every single person to silly levels. Okay, Joe Gangrel, who is hanging in a coffee bar for ...reasons... should be a man of mystery. (And odd smells.) But Stacy, who works in the same building as you and is dating Officer Marcia, the cop on the beat in your neighborhood, should not be tabula rasa.