We just "stumbled" across this entry in Wikipedia the other day .. it gives a pretty good high level overview of Instant Messaging (IM) and in particular, the use of IM for business. 

Not only are the major enterprise and consumer IM technologies outlined, but also the IM-related risks and liabilities that organisations should be aware of. 

There's also a section on IM security and archiving, which (nicely) includes figures from the Radicati Group suggesting  Akonix is a clear leader in this area.  To have a look for yourself visit:

http://en.wikipedia.org/wiki/Instant_messaging#Instant_Messaging_in_the_Business_World