Excellent thread, couldn't agree more. Luckily few of my clients IM me but those who do I IM back. Quite a few use Skype but for clients it seems to be "one off" (e.g. like a conference call) whereas for Partners we use Skype quite frequently. (Although just because Skype SAYS they are "online" they are not necessarily, their computer may be turned on and their Skype logged in but THEY may not actually be there.)
For IMPORTANT messages, believe it or not, I backup to PC and keep the log with full Date and Time, just in case of that bump on the horizon!
Elsewhere, I have to admit I initiate an IM message sometimes for really time critical communications where I believe my Client is IM savy but couldn't give any rules for this, it is just a gut feeling that they will be open to such communications. This however is ONLY ever really for thins like "Hi, hope you are well. I am in town today, any chance to meet at xx pm. Cheers, Keith" or "Hi, running 30 mins late in traffic, be there soon. Hope that is ok. Cheers, Keith".
ALL really critical communications (and certainly any attachments) will ONLY go by email, but yes I will also send an IM saying the email was sent if that is particularly a very time critical or urgent mail/attachments.
Looking forward to more posts.
Cheers

-- IM code...