Just share my $0.02.
I was once having the same predicament as you...deciding between the Olympus E510 & K10D. But in the end....i chose the K10D.;p
The (Pro) reasons (some might be mentioned in the previous post). Your mileage may vary:
1) Bigger & brighter Viewfinder
2) No need for Live view (tried liveview on the E510, dun really like it but that's me)
3) Can get a battery grip (very important to me). The grip provide a much much better grip for my (large) hand and enhance the overall "feel" of the camera. You also get a better hold of the camera while navigating the menu or pushing some buttons here and there...
4) The numbers of FA/DA etc and third party lens that you can buy without hurting your pocket (of course, i am not refering to the DA* lens with SDM)
5) Weather seal (both body & grip)
6) Good high ISO performance (upto ISO 800. 1600 looks usable IMHO) (important to me as i dun like to use flash)
7) Have top LCD display with backlight (i like)
8) Solid build and feel.
9) very customisable (as in customs functions)
10) Not heavy
Some thing to note:
1) The K10D may produced photo not suited to your liking at the default setting so you will have to play around with the color tone/setting to get the color you like.
hmmm....what have i miss....??:think:
I suggest you go down to a reputable shop to try out both camera and see which one is suitable for you.
If you are not in a hurry to get the K10D, why dun u wait for the K20D which may be available after March?