I'm in a similar boat. I have a 300D and it's served me very well, but it has some obvious flaws that can be fixed with newer offerings. Ideally I want the fictional 40D, but in the meantime I want a stop-gap. I went to a local store to try out the 400D and 30D, as they are in my price range - I would love a 5D but the wife would then have a few new handbags, and I don't think we would have the mortgage
After going hands on for 20 min in the store The major points made by both models were clear. I would like the added MP of the 400D, but it's no deal breaker, and MP doesn't make a good picture on it's own - a small point. The sensor cleaning is nice, certainly very conveient for a certain percentage of circumstanses. I, however, have already invested in the full sensor brush package and don't need any self-cleaning system. Besides, for the stubborn particles or stains, you still have to resort to conventinal methods anyway. Another small point.
The 30D however has one HUGE point and it IS a deal maker - or rather the 400D has a huge minus and deal breaker - it's WAY too small for me. I don't even have large hands, just about average. I shoot double-stacks and don't need short triggers - size XL gloves, etc. But I have no way to accurately, comfortibly hold the 400D. I had the same experience with the XT when it came out, I thought - wow that was stupid of Canon, I bet they go back after this model! Nope, too bad.
Besides that the 30D's viewfinder is a touch, but noticeably larger and brighter - something I have always wanted with my 300D. I would certainly enjoy that feature immensly! Both have exceptional rear view screens compared to the 300D, however the operation and layout of the 30D is markedly superior to the 400D. Glancing at it for settings, and the fact that the 30D body still employs the dedicated setting LCD makes it much faster, at least for someone familiar with traditional controls, over the 400D. I'm no pro, so fast easy operation is only a small point for me with the 30D, but certainly would be more cosequential to others in the industry.
Price-wise, at retail, the 400D is certainly a bargain especially to those like me that have used other exceptional bargains like our 300Ds. I for one, bought mine for less than $500 3 years ago with rebates. The 30D at retail is less so, however I like most others here do not buy near retail. The 400D being so new, in demand and often out of stock, commands full retail everywhere right now. The 30D however being in ample suppy is heavily discounted everywhere but the brick and mortor stores such as Ritz, where I was browsing for my hands on review. The $30D with expeditited shipping is less than $1175 online while the 400D is $800 (both body-only). So essentially it's down to under $400 between the two.
$400 for a much better designed/constructed body, larger more useful viewfinder and some minor features such as slightly more burst rate. However with the disadvantage (to some) of 2MP less and the absence of the cleaning feature.
I have waivered back and forth based on web reviews, stats and comments. After hands-on use, the choice was made very clear, the addional $400 would be money well spent - it's a 30D for me, at least until the 40D comes out, with hopefully the Digic III processor and more MP to put it to good use.
Oh, while I'm here I'll related a blunderous moment. This past weekend I went on my first hot air balloon ride. All in all a very nice experience, great flight, great pilot, and a handful of great shots! I have absolutely nothing to complain about except my inattention to a critical point.
I finally upgraded my walkaround lens and bought the Canon 17-85 IS. SO far so good, I really like it, although I wish I could afford faster glass - oh well, I can't. Anyway, as most know ballooning starts well before sunrise, i.e. it's dark. Before we lifted off and got in the suns rays, it was well under ideal light conditions, and I HATE using flash. Some of you can see where this is going. This was my first IS lens, and also happened to be my first time using it. Yup, I forgot to turn on IS for the WHOLE TRIP and you guessed it, about 50% of the shots have motion blur, that otherwise would have been lovely shots I deleted a couple hundred that were just garbage, and put up a small gallery here if anyone wants to see:
Balloon Flight