For us, it was a purely financial decision -- we were buying our first place and were priced out of any DC neighborhood we would have wanted to live in. We're in Rockville, which is a little farther, but I think somewhere like Bethesda or Arlington (where I lived for a while) is great. Easy access to work and the resources of the city, but a little more chill of a place to come back to. To be fair, at this point in my life I'm past the point where easily-accessible nightlife is a major factor; 5-6 years ago, I would have much rather been right in the middle of everything.

Edit: or Silver Spring! Also a great and popular "just over the border" option!