Since we are curious souls, the QuakeNet staff made a network wide CTCP version request at non-peak hour in the beginning of November 2002 that hit all connected clients at that time (don't try this at home, folks :p)

We sorted the results and present them below, for your viewing pleasure.

clients%client

52 984

63,39%

mIRC - older versions

16 344

19,55%

mIRC - v6.03

1 520

1,82%

irssi

940

1,12%

Trillian

781

0,93%

xchat

45

0,05%

BitchX

39

0,05%

ircII

18

0,02%

epic

3

0,00%

LiCe

10 907

13,05%

others

83 581 100% total

Most people seem to run a Microsoft Operating System (ie: Win95/98/ME/2000/XP), those not are listed here.

NB: Versions of mIRC prior to v6.03 may be vulnerable to security exploits, see http://worms.help.quakenet.org/mirc.php

UPDATE: An expanded list of other clients/bots and various scripts.