We get this suggestion a lot but we've been very hesitant to add it just based on our personal experience with social sites. The social flood has slowed down now, but we used to get automated invitations to social networks seemingly by the dozens every day—to the point that social spam was rivaling pitches for ******.
I appreciate the approach that you took, and I pay much closer attention to a personal email from a friend or family member than I do from an automated mass email from a website. That's why we added this FAQ:
How do I invite friends to Fuelly?
I realize it does make it a bit harder to add someone as a friend on the site, and that is a downside to our approach. But we're trying to keep everyone's email inbox as useful as possible by specifically not adding an
invite everyone I know feature. I can't say we won't ever add it, but that's our thinking up to this point.