Pre-term planning numbers are in for Harvard, and it looks like the undergrad Algorithms and Data Structures class has about 175 people planning to take the course. That's a huge jump again over the last few years (where it's jumped from the 50s to well over 100). I imagine the growth is spurred by our ever-increasing enrollment numbers in the intro classes, as well as the fact that it's being taken over by a younger, dynamic, new faculty member. (Go Jelani Nelson. I can't help but think some number of students were waiting for me to go on sabbatical...)
These numbers are usually within plus-minus 10% of the final, though there's higher variance when new instructors take over. If 175 became the steady state class size, it would mean a bit over 10% of the students at Harvard would take Algorithms at some point. I don't think I ever expected that when I started.
If we can get the people resources, at some point we'll probably want to start breaking this up. One direction is to make an "honors" class that would cover more/harder material more rapidly. (We're thinking of making this an "honors theory" course, that would cover both complexity and algorithms -- 2 classes packed into 1.) The Math department here has done this very successfully, separating out the future Putnam winners from other students early on. A benefit is it leaves the remaining students happier as well, as the curve-breakers remove themselves from the regular class. Another possibility is to do an algorithms style class designed for non-majors, that would bring in more people not currently taking algorithms as well as some of those in the current course. There are "topics" classes like this -- the Easley/Kleinberg book Networks, Crowds, and Markets: Reasoning About a Highly Connected World is algorithmic and seems to allow an instructor to choose a desired mathematical level from a broad range -- but I don't really know of examples of something more like a standard algorithms/data structures courses designed for a broader audience than for CS majors. I'd be interested in pointers to and anecdotes about experiences in such classes if they exist.