“Another way to figure out which fields are worth studying is to create the dropout graph. For example, I know many people who switched from math to computer science because they found math too hard, and no one who did the opposite. People don’t do hard things gratuitously; no one will work on a harder problem unless it is proportionately (or at least log(n)) more rewarding. So probably math is more worth studying than computer science. By similar comparisons you can make a graph of all the departments in a university. At the bottom you’ll find the subjects with least intellectual content.”
- Paul Graham

I’ve been reading a bunch of essays by Paul Graham tonight, they’re pretty good. The one linked to above has advice about grad school, too.