From my very limited experience with them (handling a couple of them), I would say that fit and finish are good, and that they were reasonably comfortable. Also, they offer a number of features that are just kind of cool as far as knives go (such as the screwdriver bits).
However, they seemed to me to be quite bulky, far more bulky than I would ever consider carrying for the fairly limited features they offer. That is, if I'm going to carry a tool for all the miscellaneous things it's got, I'm going to want it to be an efficient use of space. The Wave/Charge/etc. models fit this criterion. Leatherman's knife line does not. Another downside of the knives seems to be high susceptibility to corrosion. At least, my friend's model had rust spots; I can't say for sure what conditions he uses his knife in, but I can't imagine they're that harsh.
Ultimately, my recommendation would be to carry a Leatherman multi-tool (such as a Wave) as well as a dedicated knife (Spyderco, Benchmade, Kershaw, etc., etc.). If the two-tool carry thing isn't your cup of tea, then I would say to pick just one multi-tool and go with that. And if that's the case, I'd go with a model that has a premium steel (e.g., 154CM) for its primary blade. The Charge gets my first choice for filling such a spot (preferably Ti, XTi, or TTi, but AL or ALX would work as well). But if you want something a bit lighter, and perhaps more stripped down to the basics, like the knife line is, I'd recommend the Skeletool. Not sure if that one's out yet, or if not, when it will be released, but it would be worth checking out. From the looks of it, I'd easily go with the Skeletool over one of the models in the knife line.
Sorry if that was a little lengthy. Hopefully some of it is helpful.
Oh, and before I finish, a quick word of comparison to SAK: Ergos to me have felt fine for both, same for fit and finish. I feel like the SAK will be less prone to rust (provided you're not talking about one of the more premium Leathermans). Also, I think there are more tool options for the SAK than for the Leatherman, but I haven't checked recently to verify that. My recommendation for the Charge or Skeletool stands, though. But if neither of those appeals to you, then yes, I would go with a SAK.
Just my $0.02.