Neatest thing I've found with my smoke machine: A/C leaks. Had a customer bring me a 1996 F-350 diesel, A/C wouldn't hold a charge for more than a day or two. We don't have an electronic A/C leak detector at my shop, so I took one of the cheapie 12 inch A/C charge hoses from the parts store, cut off the end that goes to the can, stick one end to the car and one end to my smoke machine hose, smoke pours out from behind the compressor clutch. I thought it was neat, but usually only works on rather large leaks. Just make sure that the A/C system is empty first.
I also find oil leaks by pressurizing the crankcase with it (usually through the crankcase breather hose). Most recent one I found with this was a porous valve cover.
Also, you can find those annoying wind leaks if you have a diffuser. Pressurize the passenger compartment by turning the blower motor on high bringing in fresh air. The diffuser will spread the smoke and you can move it over body seams (around door weatherstripping, etc) and where the wind leak is air will be blowing out of the passenger compartment which will blow the smoke.
Just a few neat tricks. By the way, we use the Vacutec EvapPro 2000E with the roll-around cart. Great machine, and comes with great accessories.