This is the first time I've heard about airline mileage tracking sites that are similar to Mint.com, but instead of automatically logging into bank websites, they log into the airline websites to aggregate frequent flier mile balances and mileage expiration dates.
Airlines aren't happy about these services. This New York Times Bucks blog post
describes how Delta has forced one website to stop its access. Delta claimed it was slowing down their site, but it seems likely that Delta just wants to make it harder for customers to use multiple frequent flier mile programs and to maximize their miles.