How ya doin.. I have both... they both have advantages and disadvantages.
Overall I love my 721. It is definitely one of the better DVR's that dish has/had.
The only real difference that I know of is that you can drive 2 tvs independantly with the 522. Other than that the menus are slightly different.
the 522 does have some major stability issues though.
my first 522 died within 4 months. the new one should arrive today.
