I, too, think the wi-fi/IR hypothesis is pure bunk--if anything, IR would help ease, not cause wrist pain, since it's used in physiotherapy. Got my 38mm Series 2 back in June, worn w/a wide variety of bands, without incident (except inadvertently trigging Siri).
I've also had L lateral wrist pain wearing it for abt. 6 wks now, after breaking a fall with my outstretched hand. (Kids, don't try this at home). OK for a day or two, then stiffness, soreness, clicking/snapping and even metacarpal burning while late-night typing. (No visible swelling). Am a guitarist/dulcimerist, and it keeps me from gripping a guitar neck and making chords. Didn't try a brace, because not sure what kind to get. Went to walk-in ortho/sports med clinic, got X-rayed. Noticed symptoms much milder after removing the watch. No fractures or dislocation, but ortho doc says "TfCC" inflammation from a combo of the injury & a slightly-too-long ulna (bone along the outside of forearm). Radiologist noted arthritic changes--but on the thumb side (where it doesn't hurt). Ortho doc says too late to splint because that'd stiffen it more, so see if topical NSAID gel helps and get an MRI & cortisone shot in 6 wks if it doesn't.
Noticed this a.m. that I had no pain or stiffness until after wearing the watch for a minute or two. I bet it's the strap: an aftermarket leather one that is thicker & wider than the silicone and less flexy than the mesh (both Apple & aftermarket). I pushed the band higher up above the joint, which seems to help but still feels restrictive. Will go back to the orig. silicone strap and see if that's better.
Wish they made slimmer straps--or even the old "Twist-O-Flex" style.