I got an SD702 last month and have been having a ball with it. The trick is to leave milk and cookies by the fireplace. I got an AT897 shotgun mic and an AT825 stereo mic for recording sounds and bands at bars and I am about to get two AT2035's for recording small groups in more controlled locations.
After reading every post on Sound Devices' forum, it looks to me like they sell many more 722's with CF and built-in HDD than the 702 with CF only. I decided to get the 702 because it would run longer on battery without a built-in HDD, why get a digital no-moving-parts recorder and then jam a rotating spindle HDD in it and I knew it could use an external HDD.
The 702 can record to an external HDD via FW and can record to the CF and HDD, if selected, for redundancy. HOWEVER, the external HDD cannot run via FW from the 702 unless you have an external 12V battery plugged in the 702. I got that too, made it from an old video camcorder battery pack, new gell cell battery and SD power cord plug from B&H.
The 722 costs $600 more than my 702 but that difference paid for the two mics and a larger battery and a 320 GB FW HDD (on sale). I got a G-Drive mini combo with FW and USB ports so the drive allows me to hook into any SD7xx Series unit, Mac or PC. The 702 acts as a CF card reader via FW when connected to a Mac or PC, I have both and this does work on either.
Ever since I was a kid I wanted a Stellavox or Nagra tape recorder. Dad got a Revox A77 so that calmed me down for many years. This SD702 is a phenomenal piece of professional gear that although not cheap, it is not that expensive either. That Revox was $750 in 1968 which is $4400 today which is what the SD744 four track unit costs, my 702 was $1875. And this 702 totally kills any Nagra ever made and the Revox too. I hate to say that because I have great reverence for the Revox. And what does that Nagra digital unit cost, $7000?
Finally, I read many SD forum posts where professionals and amateurs alike said it was the best piece of audio equipment they ever owned in 20 years and no one had the slightest regret in buying one. A couple guys said don't spend too much time looking at other units, just get an SD 7xx and you'll never look back.