As I'm right in the middle of the query trenches and may or may not have some good news, I have been reading a lot about researching agents. There are so many of them, and first time authors (like me) have been known to just send out a query to an agent they haven't researched a whole lot about. I've actually been pretty good about researching, but once you get that "Call", you have to do a whole lot more.
I've heard a bunch of horror stories about writers who land an agent and then figure out the agent is not the best choice they could have made. I read this article from The Rejectionist blog, and I thought it was perfect. Anyone looking for or has landed an agent should read it. Very helpful in pointing out red flags. :)