My chiropractor (who is really good) recommended it after my wreck in December.

It's honestly hard to say whether it did anything for me or not, but my body did seem to hold some pretty radical adjustments with only a day or two of soreness afterward.

At least I didn't get any side effects.

Here's Sloan-Kettering's page on it. The University of Maryland doesn't have a page on boswellia, but they do reference it as a treatment for tendinitis, bursitis and arthritis.