Some excellent advice from Robert Peters in Getting What You Came For: The Smart Student’s Guide to Earning a Master’s or a Ph.D.:

If you decide to go to graduate school, don’t do it just because you don’t know what else to do,

A little later down the page:

Recognize that students who enter grad programs for specific career goals are more likely to graduate than those with vague plans.

And finally:

If you aren’t yet certain what career you want, grad school might give you insight, but there are certainly more cost-effective ways of figuring out your life.  You might be better off working for a conservation organization, teaching English overseas as a second language, or joining the Peace Corps until you’re sure what you want to do.