stinsonddog - I read the bbtracker discussion on elevation, and I think I understand the tidal vs. geodetic inaccuracy problem at a conceptual level. I don't think this is the same thing for a couple of reasons:
1. My understanding is that this inaccuracy should be rather limited in scale. In my example where I was at 4,000ft and it's showing -4,000ft, I'm off by 8,000 feet (2,500 meters). That's beyond inaccuracy to simply nowhere close.
2. When I went down the mountain, my elevation went up. E.g. back in the valley at sea level, I show within a few hundred feet of 0 elevation. No matter what your inaccuracy factor, you certainly shouldn't see your elevation go up by 4,000 feet as you go down by the same.

instamapper - If a problem with the OS, do you know if this has been reported? Seems like a fairly high impact / low complexity fix for RIM. I can ignore the minus but it makes external programs (read: Google) blow a circuit trying to interpret high-elevation paths (because they're recorded as somewhere nearer the Earth's core).