largely, I think IM is counter productive, but I use it at work to communicate with my boss, and other people that may need assistance. In that regard it is helpful, but for the most part it has no purpose except to serve as a chatting medium.

As for the insecurity of it, if You think IM is your biggest threat, then you need to rethink your security policy. If users are trained correctly in using it, and the client is configured correctly, it is no more insecure than any other internet based program. ( exluding flaws in the program that is).