I've had the 350d since they came out,(lil win on the horses sorted that out for me...) I must say I've hammered it, dropped it a few times been buried on digs, trampled by hounds, out in all sorts of weather etc etc, even had a pint spilled over it... and it's still going strong, does need sensor cleaned at the moment though !!!
As for ease of use, switch it to the green box auto and click on !!! mega easy !!! use a card reader to upload to puter...
450d my godson has one, as for a few technical differences which I wouldn't notice and it has a built in sensor cleaner, I cant see mu