I bought a Harmony remote from a "high-end audio" salesman that has a MX 700 at his house. He summed it up this way:

The MX 700 is more versatile and will do more stuff - but it is also somewhat more labor/time intensive to set up - but once it is set up it is sweet. He estimated that he had put in 20 hours (only 1 hour or so with initial set-up) playing with his to optimize the macro functions, etc. but he is the kind of guy that likes doing stuff like that. The Harmony is less versatile, but simpler - and in about 40 minutes I got it to where it runs my Sony TV and DVD player, HK receiver, old Panasonic VCR and Time-Warner cable box without any difficulties. Plus, since our home computer is a Mac, I'm pretty sure the MX 700 was not an option.