newbie = 98,900,000 hits
newcomer = 23,900,000 hits
American Heritage online, Merriam-Webster online and Dictionary.com all define "newbie" as "newcomer." The two words are synonyms. But, on the Web at least, "newbie" is four times more popular.
I don't like "newbie." It reminds me of a "Seinfeld" episode in which Elaine, flirting with Newman, calls him Newmie. Creepy.
Still, looks like I'd better get used to it.