Just finished a professional gig with an Arduino. A real Atmel chip, easy IDE (although I use vi to edit the source), gcc compiler, and a reasonable library of API calls. Already on a PCB with headers.
Only thing I don't like is the 15 mill spacing between one side of headers.
Warm fuzzy environment for teaching, and full access to the real iron for us old salts.
As one EE who has not done software for a long time, and never learned C, the Arduino is a useful self-teaching tool. And with all the spin-offs and variations and web examples it's an incredibly rich universe of toys and tools. Was fortunate enough to visit with Massimo Banzi last night, in a few weeks his University of Michigan Penny Stamps lecture will be up on the web at http://playgallery.org/playlists/stamps
OK, the Arduino is a nice thing with all the I/O figured out and a whole library of program stuff. BUT how much electronics do you learn? NOT MUCH. All about doing stuff with code, but not much about the hardware side of things. Just because you can write a comparitor program does not mean that you understand about making them stable. Sure, the kits allow folks to build neat projects, but the actual circuit theory does not get exercised very much, if at all. And in many cases usng a processor for a project would never come closw to being economically justifieable in the real world. So while it may be a fun tool to learn how microcontrollers work it certainly does not teach much about real electronics.