A trip down memory lane to see where we've been with "Rich" clients, then what makes up a "smart" client, and where we might be headed...
David Hill's WebLog : What is a Smart Client anyway?
...and from the same author, a
case study about Dell making the move towards smart clients, and loving it.
Smart Client architecture and design guide at MSDN
and
PDF version of the whole document for offline viewing
Finally, the
Smart Client Developer Center at MSDN