One of my writer pals is a YA SF author currently agented and on a multi-book deal. While I await results on multiple submissions, she tried to ease my neuroses by telling me these stats:
-She sent 66 queries out
-She had multiple R&Rs over the course of 7 months
-When she finally got an agent, she had 3 fulls out (not including previous full rejections)
-One agent sped-read and made an offer upon notice of representation. The other agent never responded and presumably still has the full in her queue two years later.

I know we all read QT and see some people go from query to offer in some insane turnaround time, like weeks instead of months and months. But I think that's the exception, not the norm. So keep chipping away at it. One of my five fulls was just rejected on Friday -- a nice rejection, but a rejection nonetheless. I'm revenge querying this morning...