Was Erica Albright real?

The existance of www.ericaalbright.com not withstanding, the name of the girl portrayed as "Erica Albright" in the film was certainly not "Erica Albright". Sorkin basically admits to this in a few interviews, where he claims to have changed three specific names and that Erica's was one of those. The person who most fits that character's depiction is a girl names Jessica Alona, but literally all anyone knows about her publicly is that Zuckerberg insulted her on LiveJournal in a drunken rant that seems to have been the start of FaceMash. The actual LiveJournal post is still available, and you can clearly see the original name in the source code for the famous "bitch" post:

http://www.slashfilm.com/the-truth-behind-the-social-network/

Note that this directly contradicts the statements made on the Erica Albright web site, which suggests that either 1) that's a fake web page, or 2) Jessica Alona has decided to go with Sorkin's pseudonym to maintain her own identity.

According to the slashfilm article, as of late 2010, no one named Jessica Alona had come forward to identify herself as the subject of that particular blog post. Also, nothing in that post necessarily claims that Zuckerberg was dating Mrs. Alona, merely that she had somehow angered him, but that does seem most likely. Note that he did not begin dating his current wife until after Facebook was already up and running, which would likely have been years after any possible relationship with the girl that inspired Facebook in the first place.

EricaAlbright.com is a hoax web site. It is just someone trying to get attention on the Internet with a "famous" name. Erica Albright is a fictitious person created for the sake of drama, because movies need a romantic plot to make them more interesting to some audience.

From http://ericaalbright.com/about/:

...By the way, everything on this website is fictional and completely made up. This website is for entertainment only and has no association with Mark Zuckerberg, Facebook, or Mark’s girlfriend depicted on the movie, The Social Network.

You can find your answer on ericaalbright.com:

I know that Mark has another girlfriend and the two of them seem very happy together. I’ve actually met her a few times when Mark and I were dating and she’s very nice. But since “The Social Network” came out, people are still asking me if him and I are going to get back together. So for once and for all, I’m going to set the record straight. I do not want to get back together with Mark. Not that there is anything wrong with him I just don’t have much in common with him. We do talk every once in a while but we’re not Facebook friends or anything. I’m not friends on FB with him mainly because I don’t want a gazillion friends on FB. (I’m not Erica Albright on FB) A lot of you have been writing to me and...

So definitely a real person (unless the website is a hoax).

EDIT (because of further reading on the website) ...

So usually I don’t read all the blogs and news sites that talk about ‘The Social Network’, but today, one just caught my attention. Maybe I’m being overly sensitive today for some reason but I just need to get a few things out in the open. The movie ‘The Social Network’ really depicts me as being a b*tch. Yeah, I know that Mark wrote that in in public HTML code which is now totally public, but I’m not really a b*tch! Do you want to know the REAL story about me, the EX Girlfriend of Mark Zuckerberg? Even though it is really cool that someone played ME in a movie, I am completely the opposite of how I am depicted in the movie. I am smart, funny, sweet (although I do have a naughty side), and I was really in LOVE with...

While not having any background information if she really existed in the way written in the movie/book or how his relationship with Priscilla actually was, I'll attempt an answer based on mere reason.

I'd say his relationship to Priscilla maybe didn't provide the same conflicts as his (maybe fictitious) relationship with Erica. While it would be wrong to say he's done everything just because of Erica, his break-up with her still serves as a major background influence to his character and the movie's story. See this related question and this one for some insight on her role in the movie. Maybe Priscilla just didn't provide those interesting developments for the story. If Erica was not real, then you have more freedom in fitting her to the story of the movie than if she had been real, like Priscilla.

EDIT: Seeing Paulster2's answer, she was indeed real. But I still stand by my reasoning, that his unsuccessful relationship with Erica was probably prefered by the writers for providing more conflict to the story and the character. In fact the movie (as well as the book) doesn't seem to be an accurate (or at least not complete) rendition of the real circumstances and characters anyway. So leaving out a character or emphasizing another one for the sake of story-telling isn't that unreasonable.

Mark did an interview and a question concerning the movie came up. He denies that the person in the movie exists at all: