I do, and would advocate that everyone else do so as well. It's easier to track movement and range (diagonal or no, it's easier on a hex grid and more consistent), it's also more natural for tactical movement. If you only play in 10 x 10 rooms and march in file, you really don't need hex. Anything else and you'll want to pick a hexmap up.
Insofar as rules that need to be modified... area of effect gets a makeover because of the way area is encompassed. Other than that, Unearthed Arcana has it all.