Pros: Great camera, great price, great pics, huge selection of Canon and 3rd party lenses
Cons: Slower 7-point auto focus system.
The bottom line: Fantastic camera for anybody looking for an entry level SLR. Take the cash saved and put it towards better lens or lenses.
Although many may assume that the latest and greatest would be the preferred route to take, don't immediately dismiss the Rebel XT 350D. This is a wonderful camera with terrific prices anywhere you look. The 400D is equally awesome, but consider the 350D body only, and putting the savings toward better "glass" (i.e. lenses). Particularly if you are on a tight budget, as I was.

Canon 350D vs 400D
A key item to note is, more Mega-Pixels means larger prints are possible, but it does not mean better pictures. 8MP will provide plenty of resolution for 8x10 prints, and the 10MP of the 400D won't give you that much more.

The Auto dust reduction system of the 400D is arguably a convenience factor, and one that many claim isn't as effective as a good old fashioned blower. It's a great feature, but far from guarantees that the sensor will never get dirty.

The main (color) LCD screen is larger on the 400D, but no longer has the monochrome info display that the 350D uses. Instead, the exposure info is displayed on the more power hungry color LCD, though I don't know what effect that has on real world battery life.

9-point Auto-Focus is one thing that gives the 400D a definitive advantage compared to the 7-point Auto-Focus of the 350D. How big that advantage is really up to the person holding it. It's not necessarily the additional 2 points, but rather the increased speed of the 9 point Auto-Focus system that improves performance. For myself, it wasn't enough to cover the price difference.

Better Glass....
I don't think I can stress this enough. I am most definitely an amateur, but embraced the advice of friends, coworkers, and that advice I found on the web. The lens or lenses you use will have drastically bigger, and far more appreciable, effect than any of the differences I noted.

Though we're talking about the "body only", the 18-55mm f/3.5-5.6 (aka. Kit Lens) that otherwise would be bundled with this, and many Canon models, is a consumer grade, entry level lens. It's a good starter lens, but there are far better options. Selecting lenses is a daunting task that I don't dare cover in any great detail here, but it is very worthwhile. There is a plethora of options out there from Canon and 3rd party manufacturers.

I opted for a Tamron 17-50mm f/2.8 that has excellent optics, it's fast, feels more solid than the "kit lens", and priced right for my budget. It also allows substantially more light into the view finder, the very first thing I noticed when I tested a friends "copy" of the kit lens.

And everybody should have the Canon 50mm f/1.8 (aka. Nifty 50). It's a prime (i.e. fixed focal length / no zoom), which does have it's limitations, but it has good optics, it's fast (large aperture), and it's CHEAP! Right around $75 every where you look.

The Camera...
In the 2 months since my purchase, I've taken over 2,000 pictures, and loved every minute of it. This is my first SLR and this level of photography is new to me. With that in mind, the various buttons and switches can be a mystery and perhaps even intimidating at first. But as I became more familiar with photography, not necessarily the camera, things appeared more intuitive. Most settings, particularly those pertaining to exposure, are one or two clicks away. I've spent infinitely more time learning more about photography than I have learning how to use the camera itself.

You can still use the camera without an intimate knowledge of how it all works as well. There's a good range of exposure modes, including Full Auto, Program mode, Portrait, Landscape, etc... and these modes work well for my wife and others.

Many of the functions and features are not unlike those found on other cameras, so I won't go into great detail about them. The camera itself feels well built and of reasonable to great quality. None of the other owners I know have had any complaints. I have fairly large hands, and it fits well in my "grip".

While I have two batteries, I've never had to swap them in the middle of using it. We recently visited the in-laws for a full week, shot 410 pictures with one battery, and still had power to spare.

Thus far, the 350D hasn't disappointed me in any way, and I am thrilled with the results. However, if I had purchased the kit, I believe I'd already feel a bit of "upgrade-itis", and shopping for something like my Tamron.