I've been trying to remix Snakes on a Plane for days. I'm listening to it on four different sound sources: pro headphones, studio monitors, computer speakers and car speakers. It sounds completely different on each one.
The headphones are a new pair (beyerdynamic DT770 Professional 80Ω); they have more bass than the Sennheiser HD280s I was using (which stops me from overcompensating and making it too boomy), but they seem to almost cancel the reverb entirely — so when I mix for them, it sounds like everything's 80 feet away from the mic when I play it on the car stereo.
The studio monitors seem to get me closer to something that'll sound good on everything, but since mixing things involves playing things over and over and over again until it's sounding the way I want it, I tend not to use them much for fear of driving Karen insane (or keeping her awake, since I frequently work on music into the wee hours). Maybe when we rent a house, I can soundproof a room, or put my studio in the basement.
Arrrgh.