In reply to gazhbo:
Ksyriums are fine wheels, light and stiff thanks to high quality metals but they are built with a finite life designed into them; the freehub runs on a plain boss machined on the hub and if you don't keep it well lubricated with fresh oil it wears the boss and eventually dies and you get the Mavic Howl of Death as it oscillates madly. Secondly, Mavic destroy all stocks of spares five years after they discontinue a model so if, like me, you've got an old Mavic rear wheel that needs a new rim, bad luck. TBH it probably isn't worth fitting a new rim anyway thanks to the freehub problem but it pains me to throw away a wheel. The front will be good for many years though, maybe I can pair it with a later gen Ksyrium.
My best, summer bike has Fulcrum Racing Zero Nite wheels, which are absolutely superb. They are light and stiff and the special finish on the rims means braking is incredibly good, as long as you use the soft blue pads and keep them very clean by wiping off accumulated dust after every ride.
Going from cheap wheels to expensive wheels makes a noticeable difference to the feel of a bike especially when cornering because better quality alloys allow greater tensions and hence a stiffer wheel. We experimented with some Superstar wheels, which only cost about £195 and were super-light and super-stiff but they wore out very fast and the rims dented for fun on Lancashire's potholes. As somebody said, you can have light, strong and cheap but only two of those qualities at any time.