For R1, I got my invite the middle of the 2nd week - and as Dee has said on her blog, invites will keep going out until the Feb. 16th.
Additionally, when I went to sign up for an interview slot, there were quite a few spots open. So all the speculation about 90% of invites going out on the first day is just that....SPECULATION. That may have been true for 2009 and 2010 applicants, but HBS is doing things very differently for 2011
So if you are still waiting for an invite, DO NOT LOSE HOPE until you get the dreaded ding email on the 16th! Best of luck to those still waiting!