The Five Fingers are nice, but with a few caveats. First, Five Fingers is the only brand that makes really nice ones, the knockoffs are garbage. Second, your feet arent used to the lack of support, generally going 'barefoot' with your footwear takes some getting used to. Third as far as climbing goes, I know some people that wear them rock climbing, but they are posers. They lack the support (last) underneath your feet that pushes pressure from your toe to your foot, so for rock climbing, unless you are
really good AND have
really strong feet, you wont be climbing anything hard in them.
All that being said, besides looking funny, they are comfortable and nice for hiking, watersports, etc. I dont own a pair, but I have worn them and my good friend Mike swears by them. I would think for tree climbing they might be nice, but only, as others said, in a rec setting. You might get away with it on prunes, if
you run the show; but where I work that dog doesnt hunt. The idea of wearing them with spikes as you likely agree doesnt make much sense.
If you do pick them up, check out this and other resources for sure. There are helpful tips on the medical/training impact of 'barefoot' activities.
http://en.wikipedia.org/wiki/Barefoot_running#Health_and_medical_implications