How about if we could post comments on friends' pages and/or individual fuel-ups? I've always wanted to put a "good job" or "quit letting the wife drive and it would be so bad!" on a few friends' fuel logs.
Yeah, I can see how that might be fun. It's not a small change, though. There are lots of things to consider when you make a feature more social than it had been previously. Right now fuel-ups fall in the category of "total ownership" by the person adding it. Anything related to a fuel-up including data, notes, tags, and everything else was added by the owner (or a select individual they "share" with). To be able to add content to a fuel-up that's not yours makes each fuel-up more of a community item than a sole-ownership item and suddenly the owner has less control over what appears in his fuel log. People would have new expectations for fuel-ups and new social anxieties, eg: Why did this fuel-up get comments and that one didn't?, Why isn't anyone commenting on my fuel-ups?, or I wish people would stop commenting every time I fuel-up.
Some people would love that and some would hate it. And even if it was a preference you could choose per fuel-up, people would see comments on fuel-ups and it would further the idea that they are community items rather than "sole-ownership" items.
We have Fuelly Mail for contacting other members. So I think a private note to someone about changes you've noticed in their mileage would be great. But we're not ready to make fuel-ups more publicly social than they already are.