Cool. Your blog might be a better place to put big chunks of code like this. Or you might throw it into PasteBin and link to it instead of pasting in here. Our forum isn't really set up to share big chunks of code.
Another vote for an API. I need the functionality of Fuelly for a site I'm planning and would happily get people signed up on Fuelly rather than re-invent the wheel, but I need access to their data on Fuelly once they have signed in on my site, so that needs an API...
phoebebright, you could ask people to upload an export of their fuelly data. All data is public here, so you could also take jcrawford27's approach and scrape the site. If you're using PHP you could even try his code.