But I was having this conversation with my dad, why upgrade just because the manufacturers have bought out a new model. Unless your camera has stopped working completely.why change it...
Dads always know best Keith.

When I returned to photography some three years ago now, I opted for Sony because of the service that I had from them as a brand when I was working, figuring out that if they had decided to enter the DSLR market the product would be right, so I bought an A100 and a couple of kit lenses, to which I added a couple of others, a wide angle and a crisper 16-80 Zeiss Sonar. The A100 did everything I wanted. After about 18 months I made the decision that I needed to upgrade, don't ask me why, I couldn't explain Why. So I bought an A700.
Did my photography improve, of course it didn't, not to any noticeable degree anyway. All I've got is a heavier lump of camera in my hand with a few more knobs on it!
The fact that other manufacturers sell more cameras than other manufacturers is the result of better marketing, publicity and PR.
Unless the A700 turns it's toes up I don't think I'll be taking the 'upgrade' trail again.
P.S. The A100 is seeing out the rest of its days converted to IR. Now that's a
regrade that I've enjoyed and found useful.