Hi Deb,
I take metformin and have had no problems with it. It is my understanding that liver problems are very rare and were strongly linked to a predecessor of metformin that was removed from the market.
It's almost a senior drug for diabetes - so many people have taken it that its side effects are well-documented by now. It is used in the treatment of PCOS, and I think it may be sold as a diet aid in Europe where it was prescribed long before the FDA allowed it to be sold here.
There's plenty of info available through Google too- if you are a pre-diabetic, you may have time to change your diet and exercise program enough to bypass the diabetes diagnosis. If you go over to 'the dark side' you'll have to do that anyhow
Best of luck to you! sandy