We are in neighboring Prince William County which I think also has an incredible school system, however Fairfax is supposed to be wonderful. Only caveats there are next year's predicted large budget cuts due to decreased home values/taxes for the county - this might affect education spending in coming years. That is probably true across a lot of high spending counties in Va.
Fairfax gifted program is pretty hard to get into, from what I have heard at least at the elementary level. If your children are really way up there you probably don't have much to worry about. I know at least one person whose child was denied eligibility not so much because of scores, but because they have a # of children accepted cutoff - basically (and this is on their website) they collect all the scores and other info, and set the gt program cutoff at a different level each year depending on the scores of kids tested that year. So one year it could be 130, the next year it could be 135.
I don't think you have to actually live in Fairfax county to get into TJ - it is a state/governor's school so kids from other counties go there as well. It is supposed to be really really great!
We also have nearby us a Tech magnet school - they have an award winning robotics team and they are sending kids to some of the elementary schools to get teams going there. There is one in a nearby elementary school that just won a lego robot design/programming contest.
The area is of course wonderful for exploring nature (mostly to the west), checking out the city, having a job that doesn't go away with the recession...the benefits are amazing. Now is a great time to move as well, outside the beltway prices for housing are way down, if you are buying.
Herndon is very interesting, it is right on the greenway for jumping into work and they have a well acclaimed gifted school there, Nysmith, grades pk-8. It is loudoun county, however, and I don't really know about their gt program in the public schools.
I wish you luck wherever you settle!
