You guys do everything the hard way. 
Computers will do this kind of thing for you. During the other thread Zeldar mentioned, I wrote some code that scrapes data like this, and as a result, I have a nearly complete dataset for answering these types of questions. It was a pretty simple matter to run it a bit more to get a picture of what’s changed in the meantime, and now I can make fascinating observations like:
Day with the most signups: April 28, 2011, with 304 signups. However, only 2 of those are still active, so lots of people who flamed out (see below) or left is less interesting than looking at the number of signups who actually stuck around for a certain amount of time, such as 60 days. Top 10 days for that:
(n = num signups, a = num still active, p = percent still active)
date n a p
2003-01-07 34 1 3
2002-03-14 35 4 11
2003-01-08 37 3 8
2003-01-09 38 1 3
2003-01-10 38 5 13
2002-03-13 39 6 15
1999-03-14 43 5 12
1999-03-11 49 7 14
2002-03-12 58 8 14
2002-03-11 107 27 25
The date with the highest number of now-banned users is, unsurprisingly, April 28, 2011 (232 banned users). The next highest is Jan 4, 2011, with 83 banned users.
The oldest banned account is Markxxx, banned after 4465 days.
I don’t have time to do more slicing and dicing at the moment, but if you have questions that can be answered by knowing everyone’s post count, total number of posts, signup date and last activity date, shoot them my way. I can also make the data available if anyone else wants to nerd out or draw graphs. One interesting graph I’ve thought of would be a line showing signups per day, with a series of lines below that indicating “stayed for a week”, “stayed for a month”, “stayed for 90 days”, etc.
Oh, one more pair of stats since it’s easy to calculate:
Top "posts per day"
11.28 Mangetout Guest
11.45 Der Trihs Member
12.17 BigT Guest
12.48 Really Not All That Bright Guest
12.95 gonzomax BANNED
13.01 John Mace Guest
15.44 Marley23 Administerminator
15.79 BrainGlutton Guest
16.91 CitizenPained Guest
17.59 Diogenes the Cynic BANNED
Top "total posts"
38830 Really Not All That Bright Guest
39401 Liberal Guest
41227 Chronos Charter Member
41805 Johnny L.A. Charter Member
41860 Guinastasia Member
42608 John Mace Guest
43518 Mangetout Guest
50390 BrainGlutton Guest
54218 Marley23 Administerminator
58797 Diogenes the Cynic BANNED