A pretty good place to grow up. Borders Loudoun County to the west, Arlington, Alexandria and DC to the east, and Prince William to the South. The Potomac runs alongside it at points.
Very well educated, and not too much crime (especially compared to DC, with Southeast DC in particular). Racially diverse as well, and also quite liberal, though that has its positive and negative side. The Washington Metro, a subway system with stops in multiple parts of VA, DC and Maryland, is a wonderful asset (though those coming from New York shouldn't expect all too much). Temperatures can get into the 90s during the summer and dip below 20 in the winter, but the summers and winters are manageable.
Unfortunately, with the high income of this area comes pretty expensive costs of living. Some teachers in Fairfax County Public Schools (a very good, but not perfect school system) have to commute from outside the county's borders. And yes, traffic can be awful. The Metro should be used as much as possible.
Are there huge differences between Fairfax County and Montgomery County (Maryland), Arlington or Alexandria? No, not really. They're all places some people would dream to raise their kids. Anyone who's ready to trash another part of the DC suburbs should remember how fortunate those people are to be near a wonderful city and in a relatively safe environment.
"So where did you go to high school?"
"Oh, in Fairfax County."
"Not bad! Be thankful for all the resources you have there. I grew up in a place with a bad school system, lots of crime and not many opportunities."