Jason Kottke puts together a thorough comparison of Blogger's early-stage growth compared to Twitter's.
From late 2001 to early 2002, Blogger doubled the number of messages in its database from 5M to 10M in under 200 days. Of course, it took Twitter just over 40 days to do the same and under 20 days to double again to 20M. The curious thing about Blogger's message growth is that large events like 9/11, SXSW 2000 & 2001, new versions of Blogger, and the launch of blog*spot didn't affect the growth at all. I expected to see a huge message spike on 9/11/01 but there was barely a blip.