I guess the answer depends on your needs for a computer in the first place.
I couldn't....I have 3-4 different machines for differing types of tasks. I can likely last a full year or more with just my 15" MBP, but even then I'd have some slowdowns when it came to renderings I have to produce for clients.
But if your needs are email, lightweight content creation and mostly content consumption...sure you could make do with either the 13" model (my preference) or the smaller 11" netbook version.