I'm interested to know what you think about this... Hopefully, I will soon be purchasing my first DSLR. I have a choice between a cheaper, entry type camera (Canon XSi) and a more advanced one (Canon 40D). However. Technology is changing so much, and fast. I know I will want to upgrade to the newer technology, even if my current camera is still good/working. My question is - how often do you guys upgrade your cameras? Are you careful with your money, and only buy when you *need* (ie. your camera is toast)? Or do you keep up with ever changing technology? Thanks!