I got WIM after I became the GM of a guild and started raid leading. The number of whispers I received got out of hand and WIM handled them nicely. It allows you to keep all your whispers organized in a separate window and it'll even keep history of conversations. One click invite and other utilities are there as well.

TESTED AND WORKING!

KNOWN ISSUES: sometimes it won't intercept incoming whispers and will let them go on your normal chat frame as well as in WIM. small problem that is totally livable.