Actually, in general, assuming you calibrate a good altimeter/barometer daily from a known reference (such as a contour line on a topo), my experience is that they're a good bit more accurate than a GPS.
As it happens, I'm currently testing several "ABC" (altimeter/barometer/compass) watches: a Suunto Core (brand new; the earlier production units had problems, but they appear to have been resolved); a Highgear Altis; and a Casio PAW-1300. I have been evaluating them alongside an old-ish Highgear Altitech (not Altitech 2) that has proven to be very accurate over the years although the compass recently quit working for some undetermined reason - I like my compasses to have a baseplate and I have not missed the digital compass at all, but YMMV).
From the point of view of baro-altimeters, I think the Altis leads in both accuracy and utility. The UI could use a little polishing but it's very flexible/configurable, has all the right data or perhaps more even than you want, and at current pricing (check C@mpmore) is an outright steal. I wish it had a better strap - that's about it.
The Core has a great UI and the firmware was programmed by someone who both understood ease of use and the English language. I absolutely love the graphic 24 hour baro display. I absolutely hate the absence of a similar display for the altimeter! It's a big watch and a good bit more expensive than either the Casio below or the Altis, especially if you want the ability to mount normal straps rather than various rubber doohickies. Accuracy is very, very good.
The Casio is actually the best watch but the worst ABC tool. The compass came out of the box off by about 45 degrees, and calibration is a manual exercise (not simply getting into calibration mode and rotating the watch - you have to set it with a map and your trusty eyeball). The barometer and altimeter require calibration much more often and its readings are much less consistent. The PAW 1300 has both solar recharge and "atomic" time sync, although radio reception is much weaker and less reliable) than the only other atomic watch I can compare it to (a Citizen).
The Highgear and Suunto don't self-sync but seem to be accurate enough (more than) for wilderness use. Solar recharge is nice, but the other two take 2032 LI button cells which are cheap, light, and have near-eternal shelf life. I typically forget where I've put the spares before they expire!
The thermometers on these suffer a good bit from being attached to your body, so be realistic about that.
From almost a decade of experience, I'd strongly recommend almost anything made by Highgear. The products are not the most stylish, but they are very accurate and dependable. I can also tell you that their customer service is not exceeded by anyone - they will go more than the extra mile for you if you need help or service. If you want a watch, I'd look at the Altis on C@mpmor's website. If you want something to clip onto your pack, consider the Altitech 2.
Edit to add: I used to have a Suunto Vector. It overlapped the Core and there's a reason I don't own it any more. The Core was much easier to use and both much more consistent and more accurate as an altimeter.
My $0.02...
