I've been watching Soylent for a while now, including following the different home-brew recipes[1].
The verdict is still out on whether you can actually live off this stuff. If you're curious about the experience, there have been a number of journalists who have gone on the stuff for a short period and wrote about it. [2][3].
EDIT: To clarify, there haven't been any long-term studies that I found on living off a nutritional shake like this and the effect that it has on your overall health. It's akin to the same stuff they feed people who won't/cannot feed themselves[4] except a lot cheaper and (hopefully) tastes better.