I upgraded from Olympus C70/C7000 Z to 400D around 6 months back. I have nothing but all praise about the camera but sometimes I find it a little restrictive in terms of following features -
Auto ISO only uses values between 100-400. Which means you cannot use preset modes in low light conditions.
No Spot Metering. My personal experience says that if you are not heavy into post-processing, spot metering is the right mode to properly expose the subject (without worrying too much about the background)
Wont let you choose metering modes in preset modes.
Grip a little small and thus tires your hands (or maybe I have big hands for the grip)
Viewfinder could have been a little more brighter
All said and done, 400D is still the BEST dSLR available for its price. Coupled with 50mm 1.4, 24-105 F4.0 L and 70-300 mm (future purchase), I don’t think I need anything more :)