I used to with a couple of people, but our corporate I.T. dept. decided IMing was too much of a security risk and blocked it. 
Only one Doper has ever IM’ed me. It was Bittersweet, and we still IM each other semi-regularly. One of these days we’ll hopefully meet in person.
Come to think of it, I’ve never tried instant messaging. Tell you what, I’ll give it a try. I’ll put my contact details in my profile in case someone fancies a chat.
I’ve got a couple of people I chat with pretty regularly; some I chat with when we’re both online at the same time, which isn’t very often; and a few others I’ll have longish conversations with when I talk to them, but that’s once a month or less. The SDMB section of my friends list is definitely the longest, though.
If you’re on Yahoo, feel free to say “hi” if you’re online. The magic password is “SDMB.” 
I’ve chatted with assorted Dopers in the past, but these days, no one messages me, and I can never think of a clever opening gambit, so I don’t bother. Plus I don’t always remember to fire up the ol’ messenger programs.
Mostly, I’m not on line as much as I used to be. But, seriously, if you catch me on line and wanna say hi, please do. If I can’t chat, I’ll tell you, but if I’m not otherwise occupied (like on the rare occasions I catch my daughter on IM) I’ll gladly natter away with you. Just tell me who you are if your user name isn’t your Dope name.
Note: FCM used to be a “talk to regularly” but these days – sniff, sniff – she’s never on (or at least never has IM on) when I am.
I run Trillian nearly all day long, but haven’t been IMed yet by any SMDB members… I guess I’m too new and don’t post enough yet to warrant it… Although I did get my first SMDB related email today… 
Fionn and I have become very good friends over IM. Cosmopolitan and I also chat quite often.