Interviewers' biggest gripe with job candidates is failure to do their homework. (Or it's among the biggest, according to HR consultant Peter Weddle.) Shouldn't you know at least something about this company? Putting that effort into the preparation can make or break your interview.
But not knowing how you did can make job candidates crazy. (Not hearing back from companies is their biggest beef.) My post "10 Must-Ask Questions for Job Seekers" touched on this, but this article at Careerealism.com advises spending half your prep time for the interview working on questions you want to ask. (It points out that often interviewers don't do the preparation a wise job-seeker will do, and hence, they might spend most of their time urging you to ask questions. You don't want to be caught without any.)
But this post at The Wise Job Search also notes that it's OK to ask how you fare. Doing so accomplishes several purposes:
It suggests asking questions such as these:
The Careerealism post also mentions that when you do follow up, you can say:
"I didn't get to convey all that I wanted to, so I hope I'll have a chance to share more in the next round."