Old thread but since the question comes up occasionally... yup, the Araya PX-45 rim (link to Araya Japan archives) was made with concave braking surface, as were several other Araya rims from that era, the early 1990s. The theory was that it provided better braking with less weight but some compromise to strength. The Araya catalog still recommended stronger double wall non-concave rims for more demanding downhill and other mountain biking activities.

My 1993 Univega Via Carisma came with the original Araya PX-45 rims. The bike was essentially marketed as what would later be called a hybrid. Good single wall rims advertised for light duty riding. Mine have held up to gravel, chipseal and rough rural pavement and some light off road riding. The rear rim was warped in a sideways skid on loose gravel over a freshly chipsealed road -- no crash, just a sideways skid and sudden stop. A bike shop mechanic was able to straighten the rim in a few minutes. Rides just fine.