I have been having back trouble for a while (started after a horrific flight delay and has come and gone ever since, 4 months now), and a friend recommended accupuncture. The therapist she really recommended didn't have an appointment till next Thursday, so I took that slot and in the meantime made a second appointment with another therapist this afternoon.

I have never had accupuncture before. Is having two treatments a week appart too much? How many treatments am I likely to need overall? Any experiences with this therapy for back trouble?

I have heard people rave about acupuncture, but have never experienced it myself. I know Newsweek did a big article about alternative healing in the past year, you might want to check their on-line archives (though you will need to register a user name with the site).
Also, check out the American Academy of Medical Acupuncture, the British Acupuncture Council and Acupuncture.com for more information.

As far as whether your appointments are well-spaced, you should ask the acupuncturist that question. S/he will be able to tell you how often you should have a treatment, based on your pain and the nature of the injury. It might be wise, though, to see only one acupuncturist as opposed to two different ones only because their techniques may vary slightly.