I know that Basecamp recently debuted reply-able email notifications for their messages subsystem. The problem is getting discussions to start on Basecamp to begin with. I'd love a mail relay service that offered configurable interaction with Basecamp's messages feature. Despite best efforts to train clients to use Basecamp messaging for important project discussions, many of those vital conversations still end up happening via normal email. After a discussion transpires via email, I'm finding that it's impractical or impossible to find time to transcribe the results back over to Basecamp for future reference.
Thus, the lazyweb request is as follows: A mail relay to handle my hashrocket.com email, which could detect conversations based on from: headers and automatically create messages on Basecamp. A slick control panel to set rules for when to create new messages would be nice. Also nice would a way of detecting how to categorize conversations.
Actually, if you want to go meta on this idea, a configurable mail processing site that let you plugin scriptable behavior would totally rock.
Theoretically, Hashrocket has the chops to build this ourselves, using an SMTP server and the Basecamp API, I just don't see us having time to do so anytime soon.