Anyways, a first cut at this is available here:
Please leave any feedback on that thread. Obviously it may likely have some kinks in it as a 1.0 version, so if you get some quirky results or issues please post the details of the title/author you tried to retrieve for and I will take a look.
An important note - as I mentioned above the FF website really is not designed for ISBN based queries. Even if you do get a match, you get taken to a page which only gives you a subset of the information we want. So rather than mess around with it I have decided for the initial release at least to only support title/author based queries. So don't go creating an empty book record with Unknown Title/Unknown Author and some ISBN value and expect this plugin to fill in the rest - it won't.