Great thread!
I've done a little research and here is what I've found:
From site:
http://3character.com/3-letter-doma...the-future.html
LLL.com buyout: early 2000
LLL.net buyout: early 2001
From another forum post it was reported (and also mentioned in the above article
LLL.info buyout: Feb. 23, 2004
LLL.biz buyout: Feb. 25, 2004