gosh, there's so much to say... too many things to take into consideration.
the benefit of having a hardtail is the efficiency, and compared to full suspensions, value. you're going to be paying more for a full suspension bike that has a certain level of components than you would for an equally spec'd hardtail.
As for full suspension, i've ridden some bikes our shop had for demo, and they took all the work out of going down trails... you just pointed the bike and that's the line you're gonna be taking, period. it was like sitting on a couch(cannondale). of course, there were SOME bikes we had in-store that just plain SUCKED... namely the Trek VRX. too heavy, too simple, too expensive.
be careful of what you're buying. try friends' bikes out. get a feel for what you would want your ideal bike to feel like, and see what you can find that's most like it...
As for myself, i've spec'd my hardtail the way i want it, and i don't see full suspension as necessary(i WAS thinking about their Stumpjumper FSR frame... the lockout fox air shock on the back really started to blur the lines between hardtail and full suspension... but "CHEAP" that frame is not).
hopefully i'll be able to ride my hardtail for as long as i live, and never fall into the "middle-aged-male-with-money-to-burn-that-gets-an-overpriced-full-suspension", stereotype.
You know what i'm talking about.