Our time there overlapped—I was a student of TimBL from 2004 to 2006, researching the Semantic Web initiative. CSAIL was, and still is, a truly magical place. I had the privilege of working alongside some of the greatest minds of our time: David Karger, Manolis Kellis, Regina Barzilay, et al an incredible assembly of brilliance.
I was there around that time, too, as an undergrad doing a UROP with Karger. It was truly a wonderful time.
That said, my favorite memory of the time is a little more low brow. One time I was waiting outside one of the single occupancy bathrooms in CSAIL for my turn to do my business. After a minute, who should come out but Tim Berners Lee himself. We carefully avoided looking at each other, as one does in this situation, and I went in and sat down.
The seat was warm! I remember sitting there grinning like an idiot thinking that my cheeks were being comforted by the residual heat of those of the creator of the world wide web.
In a similar low brow vein, I once took a wizz next to RMS in the old LCS building. When we were washing hands he tried to talk me into contributing to OpenJDK because we had previously talk a bit about a Java project I was working on for my UROP.
Karger's Randomized Algorithms class remains the only class I ever dropped at MIT. Still have PTSD from the psets for that class. Although I might have made it if it weren't for the fact that I was taking Compilers that semester, and 2 out of the 4 people in my group dropped the class. So my friend Dave and I basically had to do double the work for the final compiler implementation project.
Huh. I suppose I should see if I can join Manolis Kellis' lab; I got invited to one of the salons he hosts at his house on the quantum basis of reality and it was really fun! He also demoed a tool his lab is building for genomics knowledge graphing, and I was struck by how incredibly well-designed and empirical the whole project was.