Influences

Yesterday I posted about two former attempts at novels that I'm not ready to throw away yet. One thing which struck me as I was reading these old scrawls, was that I could tell what literature I had been reading during their writing. For the first, I could tell that I had been reading the Stephanie Plum series by Janet Evanovich due to the style of humor. In the second, I knew I had been reading a lot of Harry Potter due to the detailed descriptions. I know what I've read, but would a stranger reading my work be reminded of these other authors or see similarities? How much of what we read contains barely concealed influences on the author we're reading? At what point is a line crossed between stylistic similarities and outright theft, like what happened to this young lady?