Why the R9-285 deserves consideration at its current price point:
1) Size. Check out the size of most of the R9-285's out there, with the notably-oversized exceptions, such as the Asus STRIX. Sapphire's offering, all of XFX's 285 models, and one of HIS's models all fit neatly into a mid-tower case (such as my CoolerMaster N600) with a 200mm side fan, noting that the sides of my case do not bulge out to make room for side fans. Thus, a short and NARROW card is a definite plus.
2) Efficiency. Sure, the R9-280X might be faster, but it also requires a whopping 750W power supply-- or a minimum of 1000W if you want to run in Crossfire. The R9-285 gets close enough to that level of performance with a SUBSTANTIAL increase in efficiency, and a significant decrease in power requirements.
3) The only reason the R9-290's are so cheap right now is because they're being cleared to make room for its successor (R9-390?), which will utilize many of the Tonga architecture's efficiency improvements. When the 290's successor is released, I'm willing to bet it will be at a $450-$500 price tag.
There's also rumor of an R9-285X on the horizon, with more stream processors and a 384-bit memory controller...