How often do you use the Haas effect in your tracks? I've been using it for keyboards and separated guitars. Sometimes vox harmonies. The placement of instrumentation depends on the song for me.  I like the combination of Haas Effect and panning.
 
How or do you use it?

I don't use it much. Hit your interleave button on the master to hear why. I tend to rely on EQ and M/S compression to widen tracks, techniques that don't have mono-compatibility issues. The Haas trick can work but you've got to be careful with the delay settings: too short and you get comb filtering in mono, too long and you don't hear the Haas effect, just an echo.
 
I'm probably in the minority in this concern, though. And of course, there are certain genres where you don't have a choice as to whether to use it, because it's part of what defines the genre.