I bought a C720 myself in early January with fantasy football winnings (kind of a Christmas gift to myself).
I already have 2 Windows computers, a desktop machine I use for work and a 17" laptop, so I certainly didn't *NEED* a new computer... but the $200 price tag was very attractive, and I really wanted something lighter and more portable than the giant 17" laptop I already owned...AND that could support more "desktop" features than my Android tablet
It was kind of an experiment for me, I really just wanted to see just what a Chromebook could do, and even though I assumed I wouldn't use it all that often, I figured what the heck since it was so inexpensive.
Long story short, I absolutely love it, and am shocked by just how much I do use it. The battery life on the C720 is fantastic, it boots up in matter of seconds, it runs very smoothly, and video playback is surprisingly decent...with the HDMI output, I've even used it when traveling to stream Netflix to a TV monitor, which worked great. The C720 isn't much heavier or larger than my Nexus 10 with it's case on, so it's very easy to travel with...and it's quick boot-up times make it very easy to grab any time I need to jump online quickly. I'm even able to use the secure shell and remote desktop apps to access what I need to for work.
To be honest, I don't think that I could make a Chromebook my *ONLY* computer, but it certainly is a great compliment to what I already have...and I'll definitely be considering Chromebooks/Chromeboxes when I make purchases in the future.