Yes, Fairfax County Schools (or all schools in Virginia based on the document below) consider any vacation/family trip (even with notice to the school) an UNexcused absence. Doesn't mean you can't do it (and many do), but it won't be excused.
I know some people recommend just lying or not saying, but that's not something I want to teach my child and most elementary kids will not keep quiet about a vacation anyway. If you think the vacation is more important (and I'm not saying it isn't because most of us have been there, done that), then by all means go, but please don't misinform other parents that it won't be a problem for them if they get caught up in the school bureaucracy over unexcused absences. Just because you've gotten away with it in the past or your school didn't follow the notification rules, doesn't mean the won't start enforcing them now.
See
http://www.boarddocs.com/vsba/fairfax/Board.nsf/files/8KSQJE6808AC/$file/R2234.pdf