The replies have been very good for this thread. To me, the metering issue is the biggest pitfall to overcome when using manual aperture lenses, and it's certainly not a showstopper. By what I have read, the K10D (my camera, of course
) is the most susceptible to this issue, while all the others handle it better to some degree or another.
I have mostly experienced overexposure at smaller apertures rather than underexposure at wide apertures (this is probably because I don't have any manual lenses faster than f/2.8 yet), but you learn to compensate with a little practice. Just chimp a couple of shots and adjust your settings accordingly.