I've had an AOL IM screen name since the late 90's (askcalif) For awhile I was using it a lot to chat with friends and relatives. I also had an ICQ number, but only used it for a couple of months. The last couple of years I didn't bother even opening up chat in the evenings when I turned on my home computer to check email. I just got a new computer and haven't bothered to install the AIM software and may not for quite awhile.
In considering this change in usage I'm wondering what factors are different between then and now. One major one is long-distance phone costs. I used to use AIM instead of calling out-of-town friends and family. Then in 2001 or 2002 I got a wireless phone service that includes long distance and no roaming, etc. Since the calls are already paid for I prefer hearing voices than typing conversations.
Regarding IM for library service, if it is being used by our patrons then resources should be devoted to it. Cost-benefits should be periodically analysed. In addition there may be network security implications of running IM chats. Most of the IT security trade journals caution businesses about the risks of IM. Viruses and trojans have been spread through IM.
Our library will soon be installing a web filtering software product, mainly to filter out malicious sites. Most institutions using the software block AIM, Yahoo Chat, Meebo, etc. Some of our IT people want to turn on the blocking of chat services. For non-public service areas it may be appropriate (should the HR staff be IM'ing their friends during work hours?) but we have to be careful not to inhibit the reference desks from providing service.