My purchase is usually driven by the old thing not meeting my needs anymore. Of course, one thing leads to another which leads to another...
Case in point: I got a Canon 10D two months ago, leaping from film to digital. I realised that all the slides I was shooting were just getting scanned in anyway, and I was wasting a ton of time cleaning up the slides in Photoshop because of dust and crap. I figured I could either buy a really good film scanner, or just get a digital camera
Of course, a month later I ran out of space on my antiquated 30GB hard drive. This, coupled with the grand opening of Fry's downtown (oh dear) lead to a new 160GB drive.
Then I realised that I had Photoshop 5.0, and there were a few subtle things I wished it did. So I upgraded to Photoshop 7. And a Wacom tablet (a cheap one!) to give me better precision while editing.
This weekend I was using Photoshop to edit a 31MB TIFF file, and I realised waiting 5 minutes for the picture to load sucks. My Athlon 600MHz lasted me 3 years, but it was time for an upgrade. That, coupled with the new Fry's downtown, and I convinced myself I needed a new motherboard and CPU. Of course, the RAM is totally different than my old RAM, so I needed new RAM too.
It never ends... Jason, once you get that Digital Rebel, you don't know what you're in for 8O