Here comes the voice of experience!
Back in the day when I had finished uni, my hair was halfway down my back, and I was looking for graduate jobs. I went to many interviews, and always had it clean, and always had it tied back neatly (so I looked like an IT geek). I didn't get any jobs.
Then one day I went to an interview. I still had my long hair. At the end of the interview, the interviewer said "You don't have this job, and I think that if you're ever going to find a job you should get your hair cut. First impressions cound for a lot, and long hair doesn't leave a good first impression". (These may not have been the exact words, but he didn't mince any words, and definately said "get a haircut").
So I got a haircut, and got the very next job I applied for, and was offered another one about an hour after I accepted it as well.
Basically, it's a tight market out there at the moment, and if getting a job is a priority (and from the sounds of things in other threads, it may well be), you are not going to do yourself a disservice by getting it cut.
And anyway, once you entrench yourself in the job and show them how good you are, you can always grow it back.