I would not feel comfortable with the idea that Microsoft or Yahoo could take our content, make an encyclopedia out of it (redistributable, of course), and *not* include an invariant section amounting to a link back to us.
Do others share this sentiment?
I'll be the token dissenter here. I certainly don't care what anyone else does with free content--that's why I made it free in the first place, because my imagination for what uses it might be put to is limited. Let any take it for any reason--for free or for profit--as long as they don't commit outright fraud by claiming that they created it and attach their own copyright notice, it's still free.
In support of the general idea, though, I should point out that making the requirement doesn't actually prevent any other uses, it just makes them non-automatic. Bomis could still grant permission for uses that violated the GFDL on an individual basis. 0