In case you missed Laurence Hart's comment, the ACM paper gave this breakdown:

Fun: 6.1
Ideology: 5.6
Values: 4.0
Understanding: 3.9
Enhancement: 3.0
Protective: 2.0
Career: 1.7
Social: 1.5

That's doesn't totally jive with the above breakdown (what's "protective?") but interesting nonetheless. Fun and ideology trump personal and professional glory... or any social concerns.

In a strange, strange way, Wikipedians are actually selfish!

I'm sure some meme-head is going to take this to the next level...