According to the 2008 annual report (sorry, most updated online I could find), the helicopter performed 2,364 missions, did 128 medevacs, and was in the air for over 1100 hrs. I'm assuming that for the most part, that was working aerial support for burglaries, shootings, foot chases and pursuits. As for the medevacs, I'm fairly confident if a person is getting taken to the hospital in a helicopter over an ambulance, it's because their life is in serious jeopardy. So I think it's safe to assume 128 or so lives were either saved or attempted to be saved via the helicopter.
http://www.fairfaxcounty.gov/police/inside-fcpd/pdf/fcpd_ar08_web.pdf
Look, I get that the majority of people on here hate cops. Whatever your reason, I don't really give a shit, it's your reason. I've had a couple of run-ins with county cops, one I thought was a bit nit-picky but I was treated fairly because I didn't act like an asshole to the guy, and at least one I know I earned because I was hammered and acting dumb and still got cut a break because I acted respectfully and got to go home with a friend. Bottom line, spare me the bitching and moaning about funding a fucking helicopter for the police force. Most major cities PDs have one, so I don't really think it's an issue that the richest/2nd richest county in the entire country has a helicopter. If some asshole breaks into my house in the middle of the night, I'm actually pretty happy that there is a helicopter here that will try and find him as he runs off like the little bitch he is. And the majority of people on here either don't pay taxes or pay so little who gives a crap. Paying taxes doesn't give you the authority to either decide or act like you know how to run a police force from your couch or because you saw an episode of The Wire one time.
And last I heard the "navy" as you put it doesn't even operate anymore because of the budget problems. I think it consisted of one boat....again, who gives a shit? People on a lake get hammered or have boating problems and need assistance. I'm pretty sure that's what cops are supposed to do. You want them to use a canoe or a paddleboat? Get over yourself.