People (myself included) have asked more than once in these forums for a mastic remover for old tile. I found a product last year at Menards that did the trick, but summer came and went and never got around to using it (since it has to be completely vented when using the stuff).
Anyways, someone recommended this product:
http://www.franmar.com/mastic.html
which is soy-based mastic remover. Completely non toxic with no fumes to worry about, so you can use it anytime while people are around or not.
I asked for a sample and tried it out and just wanted to say that this product works great, though you probably need two applications. I have no affiliation with the company…just a happy customer (well, I will be a customer once I order the larger supply).