I tend to agree with John, but I do see in this digital imaging age (that has yet to reach full maturity) how the temptation to upgrade is greater. With film, if you had a good, expandable camera and lens system, there's not much reason to upgrade/change. The film stock was more or less the upgradeable component. With D-SLRs advances are continuing to achieve comparable results to film but it's all tied to the image sensor in the camera; you can't upgrade the image sensor without upgrading the camera body.
That said, I've been shooting with the original Canon Digital Rebel for the last five years and only recently saw a reason to upgrade to the 40d. Even then I feel like it's a bit of a luxury purchase since I've been able to get around the absence of features like spot metering and even learned to tolerate the stupid Ai focus mode.
While a part of me definitely loves the gadgetry and cool factor of the gear, the gear doesn't make the photograph. How many of us have been offended when someone sees our photographs and says, "Wow, you must have a good camera!" In some ways when we go gear-crazy we are enabling or supporting these kinds of comments. I don't say this to lecture or be snobbish toward anyone - it's something I struggle with personally and must constantly remind myself of. And actually when I joined Flickr and started perusing that network, I came across a photographer who was a perfect example of the gear being unimportant. I found her because I was surfing through other users of an old Canon 1.3 MP point-and-shoot I used to own - that's what she was using for her earliest stuff and her photographic eye was just amazing.
Check her out - she's an inspiration.
EDIT: Actually, she's still using that Powershot A10!