I'm really lazy and don't really care about food either way (I mean, I love eating, but my favorite foods are simple things and I could eat the same 4 things over and over and be pretty happy about that), so the idea of Soylent is tempting. I mean, yeah, I can microwave a frozen meal, that's easy, but it's also not that good for me. Even if it's Weight Watchers and not high in calories or whatever, it's got way too much sodium, etc. This would be better (presumably) than easy, processed food. Which is what the really busy people are eating, if they're not doing something even worse and eating fast food.
I think the best use of it would be to eat less than an entire day's worth of it for breakfast/lunch, then make one real, delicious thing for dinner. I mean, I've been making smoothies for breakfast in an attempt to eat more fruits/veggies; this really isn't that different (except for the lack of tasting like something).
I'd imagine that if this started getting popular, people would want mixes that tasted like something, though, so they'd have to come out with a line of foods with different flavors.