This is something I think about a lot, Kevin - the way it works in my classes is that every week there is a kind of smorgasbord of activities. All are open, but some are more interactive than others, and some students do indeed gravitate towards making different kinds of choices. There are always some students who really like reading comments on other people's stuff and getting comments back, while other students less so (or maybe they really like interacting about their project, but not so much about their blog posts, etc.). I'd actually offer even more choices except that of course you run into the problem of people being overwhelmed with choices, ha ha.
And as for privacy issues, I always offer the option of anonymous/pseudonymous participation, but no student has ever chosen that (although some people do choose to not include their name on their class project website). I suspect it is because all my students are regular Univ. of Oklahoma students who are just take this one class online, and the rest of their classes are in a regular classroom. So, in the same way that you probably wouldn't wear a paper bag over your head or use a pseudonym in a regular classroom, they don't seem to feel the need to do that online, and they really bring to my online classes the same good social impulses that they feel in their face to face classes. The social interaction part of the class is a big plus in terms of their engagement and motivation, and I love watching that happen!
The openness thing (creating blogs and websites as opposed to just staying in the D2L prison cell) doesn't seem to faze them at all, although of course if anyone wants an anonymous or pseudonymous option, that's totally cool with me. And I always use an animal avatar myself so they can see they don't need to use a personal photo if they don't want to.