If you're itching to upgrade you Canon dSLR, especially if you've had an EOS 350d / Rebel XT and you're looking at a 600d / T3i, then here's my advice.
Firstly, don't upgrade thinking that your photos will look better. In nice light, which most of us amateurs like taking photos in, there is no discernable difference between the 350d and the 600d. The 350d / Rebel XT takes photographs that are good enough to pass the moderators at Istock photo - which means they're good enough for professional use.
Sure, there's more megapixels, 8 vs 18, which means that you can crop in further, but if you get your framing right in camera it doesn't matter anyway. Remember that if you upscale your image in Photoshop (or Elements) you can print out an 8 megapixelphoto to huge sizes that look still great.
Higher ISO performance can be a red herring too. It's nice to be able to shoot indoors at ISO 3200, and the photos look reasonably clean, but wouldn't you be shooting with an external flash to get the best results?
You may be reading this thinking that I'm regretting upgrading to the Canon EOS 600d, but nothing could be further from the truth. My 350d was getting tired (the viewfinder display stopped working months ago), but that wouldn't be a justification for spending £400. Having a new camera has invigorated my shooting, I've been thinking about approaching my subjects in a different way, and the 600d / T3i has surprised me with the following three marvelous features:
1) The articulated screen. Let's not beat around the bush, this 3" beauty that swings around, pivots and dazzles with its clarity, colour and sharpness, is so much better than the postage stamp on the back of my old 350d / XT that it's worth the price of admission alone.
2) Auto ISO. Wow, this feature is amazing. The camera now looks after you, making sure that your shutter speed won't drop low enough to introduce camera shake, eliminating 90% of those blurry shots which are so disappointing when you come to review your images. Auto ISO means that manual mode is for everyone - just choose your depth of field (aperture) and shutter speed (how much subject blur you want) and the camera will adjust the ISO to get a correct exposure. Magic.
3) 1080 HD Video. Yes, I'm a stills photographer, but I've fallen in love with the moving image. This camera gives us the ability to shoot broadcast quality video, at the cinematic 24fps, with our wonderful small depth of field Canon lenses. I'm not talking about creating long movies, but how about the idea of the "long photograph" - where you capture a scene, not a 1/125th of a second, but for 60 seconds, a just-moving vista that might be mistaken for a photograph, but something is moving, the ripple of water, the wave of the grass or the setting of the Sun. A whole new genre? Perhaps.
I hope this article and video encourages you to upgrade your camera, just do it for the right reasons and with the right expectations.