Beautiful, powerful, great handling bikes (I don't know about parts availability, but if they are as bad as for the 2005 MV Agusta F4-1000s I had, I wouldn't buy it for just that reason!). There's a black 2004 Haga/Edwards replica at the shop here where I live with 285 miles on the odometer that they'd take $7000 for! I wish I needed another bike !
i've never tried the bike, but i can talk of the Bike Maker. Aprilia's bike are Really good, i've tried an rs125 and it uses quality materials (even if it is only a 125) (obviously not at the level of a superbike or 125 gp ) and it hasn't much tecnichal problems, i've done nothing in 20k km (only ordinary operations such as cleaning the exhaust partializer valve) and the bike is still running well.
But if something goes wrong and you have a slide (nothing serious, you just broke a staff (the triangle that supports the place where you put your feet, i don't know how it's in english)), you are going to spend lot of money... for the staff of a 125 Aprilia asks 40€... spare parts from aprilia are VERY expensive. another example, for a cilinder (125) they asked 600€, and 180 for a piston when an aftermaket cilinder (160 but fits on 125 block) you spend 400€ with piston included, or 90€ for a spare piston...
But You can always find parts on ebay, aprilia's are common bike here in italy so there are lot's of parts at decent prices!!
I've ridden both the early and later versions of the RSV Mille and they are well built, fast, smooth, with sublime handling but for my tastes don't "feel" as satisfying as the Ducati competition. The later 04 -08 version trades a little bottom end for more top end hit but I like the early engine characteristics better. The engines built by Rotax are definately reliable. My close cousin Aprilia Falco - basically an RSV engine in a different frame - has 50,000 mostly trouble free miles.