To weigh in myself...
I'm a Mechanical Engineer (BS from Michigan State, MS and PhD from University of Minnesota), and I've rather enjoyed my career so far (I work as an R+D engineer for a small consulting company (
http://www.creare.com).
I chose mechanical engineering because I really liked the mechanical and thermal aspects of physics and chemistry, and thought that fluid mechanics, heat transfer, control theory, and vibrations would be interesting to study (and, in fact, they were). That, and I've always had a natural talent for the sort of math and analytical skills that are used heavily in engineering. I also grew up as the sort of kid who spent half his spare time helping my father eek a few extra years out of our family's beat-up cars...
Note that there is a lot of overlap between types of engineers, especially at the undergraduate level. When I was getting my BS degree, the classes that interested me the most (heat transfer and fluid mechanics) were taught almost identically in the Chemical Engineering and Civil Engineering departments, and most of the other classes had similar versions in other departments (Controls taught in both EE and ME, for example, although the applications were much different). Part of being a good engineer is being flexible and having a wide variety of useful analytical skills, so this shouldn't be surprising (and note that, unless they've changed things, some of the tests like the EIT/FE exam aren't discipline specific, so it helps to be broad in your choice of classes).
As far as the value of a degree, I work with a number of engineers, with backgrounds spanning from no degree up to PhDs, and I can say that to a large extent education does matter, but so is experience, and neither can really substitute for the other. There are few substitutes for the learning that accompanies dedicating a few years of your life to a PhD (which, for me and most of my colleagues was easily a 16-hour-a-day job for a few years). And there are few substitutes for having 5 years of experience in the Real World[tm] tucked under your belt. But they are different, and try not to underestimate either one
A lot of people ask me about why I got a PhD; indeed, getting degrees beyond the Masters for an engineer doesn't usually turn into immediate increase in compensation, indeed, after getting my PhD I got fewer job offers than I did when I finished my MS, and the salary wasn't much different than what I would've been making had I been working those years, but the quality and type of job offers were better (i.e. the work was more interesting, and job advancement possibilities seem a bit better).