You would only need one DVR because it has two tuners (1 HD and 1 SD) And Finally, VOD does cost extra ($6.99 for HD rental)
Note.. the 722k has two tuners both HD, the *outputs* are HD for TV1 (1 HDMI, 1 Component, and 1 SD Composite output sets), and SD for TV2, with the SD being available as standard coax cable out and RCA V/L+R out (composite out).
Many VOD itemss are at an additional fee, with SD to HD offerings from 99 cents up to $6.99 for a full length movie. There are very few VOD items available free of charge, most of a negligible value ... some 5 minute videos related to travel & destinations, there is a preview up there for something about Tron Legacy or the making of, etc.. but most aren't worth the cost in $ or time to get access to. Much of the VOD offering for TV shows & Movies at higher bit rates either take too long to download (or need to be started and then you come back later) or are so very slow in overall download speed that it frustrates many people.
Dish is also working on their "DishOnline.Com" offering which is similar to Hulu, and appears to try to offer content that mirrors your available programming.
And lastly ... with the 722k, it is one of the receivers capable of supporting the SlingAdapter (99 dollars on dish's site) with it, in working order, you get an option to watch anything on your 722k anywhere you have high speed internet. It works sufficiently that 99 isn't a bad upgrade option. The 99 dollars is currently a one time fee, the adapter takes over "TV2" when in use, and there is currently no per monthly cost to using Dish's apps for the slingadapter (SlingAdapter as opposed to a full utility Sling Box, whis is a one time purchase, but currently requires a monthly fee to maintain web access for them, again the full SlingBox not SlingAdapter)
Oh and one more thing ... the 722k has a module bay, which allows you to purchase and install an OTA (over the air) module that you could attach to an old fashioned arial, to receive broadcast TV independently of "Locals" from the Satellite. With one of those OTA Modules, you can then record upto 4 stations at once (2 Satellites, 2 OTA)
Of the biggest drawbacks of the 722k ... currently only use 500G hard drives, so you get only 55hrs HD or 300+ hours of SD recording. You can hook up an External Hard Drive ("EHD") and move recordings ... but currently you can't record directly to the drive, you can play from the external drive though, and if you had two 722k's on your account, you could move the external hard drive from 722k to 722k.
I think that about covers all of it so far.. wish lists, are something else..