The problems related to fosamax are mainly for those who take it every day, or don't take it as directed. If you start treatment early enough it is only one tablet a week so I can't see how it can be that risky.
I'm proof that it definitely helps. I was diagnosed with osteopenia probably about 8 years ago and I started taking fosamax. I didn't need hrt then, and my bone density improved. About two years later I was scared off it by a naturopath, and for the next four years my density gradually got worse even though I was now using hrt. I've been back on fosamax for the last two years and there has been a big improvement.
My attitude is that if you read enough stuff on the internet you would scare yourself off all medications. Just take hrt as an example. People pull up a lot of "studies" to prove their particular POV.
I watched my father battle osteoporosis, a broken hip and a very painful final six months. I'll take my chances with fosamax.
*edit* I'll just quickly add that Dr Elizabeth Vliet recommends the use of Fosamax in her book "Screaming to be Heard", so I'll take her opinion over what you read on the internet. My own GP is also very happy to prescribe it. There may come a point where I might be able to stop taking it for a while, if the density has improved enough, but I will be reluctant to stop it long term because it will just decline again, and I don't want that to happen.