Many people use instant message as more of a tool to catalogue information than a place to have an active discussion. This leads to a lot of wasted time and frustration
The most important trait to consider when using IM software is that it is ephemeral, and must be treated as such.
Core Ideas
You should not "catch up" on discussions
Move important information to a different location
Don't expect people to be "in the know" for a discussion they weren't present for
try to give all of the information to a question at once, because instant messaging is asynchronous and should be treated as such