EgroThe real advantage of this keyboard is how customizable it is, allowing for layering of multiple layouts and macros, as well as the options for any cherry switch or some ALPS switches. There are also a couple of extra keys (compared to the HHKB 2). Many people are also fans of the Hacker (Japanese) layout that is difficult to find in other keyboards.
The main disadvantage is that since it is a custom layout it will be harder to find keysets for it outside of massdrop. Some people don't like the case/stand that comes with it, supposedly the next round will have a normal mounting plate so it can be put in a standard 60% case.