I just found out from reading a review on another blog that one of the gothic fantasy novels out this year has a major plotline that is similar to a minor one in T. "Very fresh," says the reviewer. And yeah, I'd thought so too. Sigh.
Authors go through this all the time. I guess the fear is that you'll seem derivative, even though the your book is already well in progress or under contract or, in my case, in production--especially because publishing time bears no discernable relationship to real-world time (AKA when an editor says "two weeks," that means "someday, eventually").
What's making me feel better is that I've actually been through this before. My debut novel had what I thought were similarities to one by a fave writer of mine (and was released the season before), plus both covers featured a picture of a girl with a camera.
As far as I could tell, nobody but us noticed, though I did enthusiastically recommend to readers who enjoyed mine that they try hers.