In other cases, I had a full manuscript under consideration when the author notified me that they had an offer on the table. I read the manuscript and in some cases, chose to step aside for an agent who obviously felt more strongly about it than I did. Fast-forwarded several months, and a name in PM sounds familiar. I look it up, and sure enough, it's someone who queried me-- with an earlier project.
To me, it's this situation that is forever a reminder of how tough it can be to break in--and how important it is to stick with it and keep writing. For whatever reason, that first project didn't sell--but the second one did. One in the last few weeks actually was a major deal (READ: Over 500K).
I signed my agent based on a project that didn't sell. PRADA & PREJUDICE was the second one to go on submissions.
I'm not saying all this to make it sound as if your first agented project won't sell-- those ones sell all the time too!--but to remember that publishing is sometimes just a process, and that luck and timing play into it too, so sticking with it and continuing to write is the best thing you can do for your career.