Very useful for sites like Quora who do not understand that some users don't want to use their real life identity.
The "why should I have to give you X before you'll give me Y? - here have junk instead" thing is wrong IMO. You don't have to give them X, you have the option of going elsewhere or simply living without Y. Why should they give you Y without you providing X if they don't want to? Their house, their rules.
Voting with your feet is more likely to have some effect than providing fake information will.
That's an interesting opinion. However, this isn't just "their house." They chose to provide their site as part of the Web, and some of us believe that means they'll have to cope with the broader community's norms and traditions, too, including anonymity and pseudonymity.
I had the same debate regarding open-ended questions on the stack exchange network a while back, and as a result moved to Quora. But no site is perfect.