Where is the line between that you really need and what you just think you need?
I have a very nice camera for my photography business. It’s a Rebel XT, 8MP. It cost me about $900. I have two lenses for it. Both of them were about $250 each. That’s about $1400 in camera gear that I use on a pretty much daily basis. It’s also a 1.6 crop factor camera, which means my 35mm lens acts like a 50mm and my 55mm lens acts like an 85mm. This is fine. I like the way they work. I’m mostly happy with the camera now, but there are two things it’s lacking that are making a difference in my work. One is spot metering, the other is more MP. With this camera, it’s hard to shoot against the sun, and I can’t enlarge prints more than 20×24. The XT is rated for about 25,000 shutter clicks, and I have 16,000 on it now. It has a real shutter that bangs on one side of the camera when the button is pressed, and it will eventually bang itself to pieces inside the camera. It’s not a fixable situation. So, eventually, I’ll need to buy a new camera. This is the problem. I’ve narrowed it down to three models.

Rebel XTi- Good: 10MP, light and small, same funtions as the one I use now, easy to learn, 1.6 crop factor so my lenses would fit on it. Bad: No spot metering, 25,000 clicks. Price: $700

30D- Good: Has spot metering, has a bunch of other functions that mine lacks, semi-small body, easy to learn, 1.6 crop so able to use my lenses, 100,000 clicks. Bad: only 8MP, same as my current camera. Price: $1250

5D- Good: Full-frame camera means that it’s sharp as hell, 200,000 clicks, very very low noise at high ISO’s, has spot metering, has a lot of other awesome funtions, 12MP. Bad: Full-frame camera means that my lenses act like the 35 and 55 they are (so I’d have to sell the 35 and buy an 85), huge and heavy body. Price: $2700

So… I WANT the 5D, but do I really NEED it? The 85mm lens I want to go with it is $1800 all by itself, bringing the 5D price up to a total of $4500. Not bad for something I’d use for 5 years or so, but woof on the upfront costs. My business is not exactly suffering because of the lower-end camera I use, but I really could do so much more with the 5D. Not like any of this would come to fruition any time soon. We’re still trying to scrape up enough to get to NY.
It doesn’t help that 3 people on my list have just bought the Nikon d200 in the past week. I’m in serious hardware envy over here. I want to bite things.