If they do this, it could be huge. BUT, they need to make a clear incentive to do so - the iPhone app market is growing so quickly because people are reading the stories of $30.000 in a weekend and all that. If there is a clear way of making money on an email app, Yahoo will have a slew of apps, and this could solve one of the larger problems we are facing right now - email overload.

But for this to be effective, email has to be personalised also. Yahoo mail is inferior to gmail in that the experience feels a lot more like you are visiting a yahoo site, and not visiting your email box. That needs to change.