The eBay stuff is also pre-painted, but not to match the original colors, so it would have to be painted anyway. If you decide, "Heck with it, I'll use the color it came in," then your tank is the wrong color.
Since you have to paint something, you may as well have your original panel painted after a repair. That repair has got to be cheaper than buying panels you don't need.
The only thing the eBay panels are cheaper than is Yamaha panels, and by the time you paint them, I don't know if that's true any more, since the Yamaha panels come painted and stickered to original colors.
After my lowside in gravel back in October '07, the Progressive guy called the local dealer for prices, wrote me a check for their price plus labor, and of course I ordered genuine panels online for less and installed them myself. Because my bike slid under an Aarmco barrier it damged both sides, the fender, cowl, and windshield, so I got all new plastic from the pegs forward. (Price difference made up the deductible. And then some.)