If you have two receivers, the "two output" aspect of the 522/625 turns out to be meaningless (unless, of course, you need 3 or 4 independent TV viewing locations).
For example, I have a 721 and a 501, and I can see either one on either TV on the RF cable.
The 522/625 only has one S-Video output and one digital audio output, so it only supports one high quality TV.
A 721 and a 501/508 gives you 3 tuners for a dollar or two less a month than one 522/625.
After having two 501s for a long while, I found that I kept coming across situations where two tuners was not enough. Somehow, channels seems to be expert at scheduling the best shows at the same time, with nothing good on other days.
What's right for each household is different, but I thought I would bring up these aspects (since someone asked for opinions).