Chrome's learning curve is effectively zero – if you've used a browser, you know how to use Chrome – and it runs very quickly, even on fairly modest hardware. If you're a paid-up fan of cloud-based apps Chrome is a very affordable and elegant way to access them.
Chrome's simplicity means it can't do many of the things you'd expect small laptops to do, and while Google's own apps are very good you may find that key apps you want to use aren't available for the platform. If you're a long-time laptop user you might find the simplicity more restrictive than refreshing.
If Steve Jobs was right and PCs are trucks and tablets are cars, where does that leave Chromebooks? We'd suggest that they're like bikes. They're simple, lightweight, nippy and come at a fraction of the price of their rivals, and while you wouldn't want to carry an IKEA wardrobe on one they're fantastic for everyday commuting.
Chrome can't replace a mobile video workstation or scientific number cruncher, but it isn't trying to: it's designed to be a thin client for everyday apps, and it does that job admirably. It makes most sense in corporate or educational environments where users only need a handful of essential apps, but it's an excellent low-cost alternative to a tablet or indeed Ultrabook.