I don't have fantastic numbers by any stretch of the imagination, but enough that I applied to USC as one of my more "sure things." Applied in November, complete early December. Radio silence.
What everyone has posted makes sense, but I really don't understand their process. Why go at a snails pace? Until I get accepted to a school, I don't focus on it too much. With other schools that have accepted me, I've planned out attending ASW, emailed some current/former students, gotten a decent idea of scholarship/COL, etc. It seems like it's only to USC's detriment to have people wait so long. Maybe they want people to withdraw once they know they wouldn't go no matter what. I don't know.
It makes sense if you're YHS, but otherwise? Maybe it goes a long way to explaining their 20% yield vs. UCLA's 30% (pure conjecture).
I was thinking about this exact thing earlier when I was looking at USC's graph on LSN. It's no secret that the earlier you get accepted to a school, the more time you have to think about it, and the more likely you are to subconsciously commit to it. I see it happening to myself even though I know I have several schools I've yet to hear from. Considering that the applicants that USC has already admitted pretty much all have highly competitive numbers that should get them accepted to equally competitive as well as more competitive schools, it does seem a little destructive to have only accepted them this late in the game. (That's comparatively, of course, as there is still plenty of time left in this cycle.) Hence, the yield issue.
However, if the extra time is taken to give softs, or whatever, more consideration, maybe it is a good thing. I don't love it when schools make their decisions solely based on numbers, so taking some extra time may be more beneficial for the class at large.