I agree that email should be made simpler but I don't think Xobni has done anything interesting yet. I am excited for what they'll come up with because the interface looked really neat and email definitely could be improved.
If they took all that information and made it more seamless into the email they would really have something. This almost certainly requires changing the whole interface. Being only a sidebar in outlook is limited right from the get-go. Outlook still sucked even with xobni installed.
I found Xobni's stats feature useful - especially the data on what time of day specific people have written or responded to you before. I've used this feature to optimize the timing of communications with clients and bosses, but other than that it doesn't really solve the email overload problem. Yet, I hope.
If they took all that information and made it more seamless into the email they would really have something. This almost certainly requires changing the whole interface. Being only a sidebar in outlook is limited right from the get-go. Outlook still sucked even with xobni installed.