Editor Stanley Schmidt posted an old editorial he wrote about accepting and rejecting serial novels for Analog magazine.
I found this interesting, but it would have been more help to me back in 2002. Back then, my publisher put the StarDoc series on hold and instead had me write SF standalones for hardcover. My editor at that time suggested I submit StarDoc book six to Mr. Schmidt for serialization in his magazine.
I queried Analog and received a form letter approving a synopsis submission. I submitted the synopsis, and received a form letter rejection (I stress the form letters because a lot of aspiring writers think published authors don't get them. We do.)
This past spring I sold StarDoc book six, Rebel Ice, plus book seven, ClanSon to a different editor at Roc. This was nice as I signed for a lot more money than Analog would have paid me.
Another example: Gordon Van Gelder has rejected every short story I've submitted to F&SF (just FYI, he did brief but personal rejections as opposed to the form letter.) I later developed two of those stories into the Darkyn novels, three of which I also sold this past spring to Signet Eclipse. Also made a great deal more $$$ with the book sales than the short stories would have brought in.
Moral of the stories: A rejection doesn't mean your work can't sell. It only means it won't sell to that particular editor. Sometimes, they may even be doing you a favor.