Ok guys, take this for what it's worth, but I scoured through the old threads regarding interview invites and here's what I came up with:
Fall 2010 Rd 1: 2 major waves with each wave trickling out across 3-5 days (10/23/2009-10/29/2009ish) then 11/10/2009-11/12/2009ish.
Fall 2010 Rd 2: Trickled out between 2/1/2010-2/18/2010 with a couple hotter spots on 2/1 and 2/11.
Fall 2011 Rd 1: 2 major waves on first and last day of interview period (as many have noted)
Fall 2011 Rd 2: 3 major waves on first, middle Friday, and last day of interview period
If nothing else, looking at these suggest there are probably many, many more invites to come. So sit back and enjoy losing your lunch on this ride! (I left out Rd3s since they’re less representative of the other 2 rounds).