I don't agree with everything that Alex Payne writes in his latest blog post (I think there's a lot of potential in PostBox and Gmail's lack of inline messages is a major barrier for me) but he's spot on that email is caught in a strange time warp. There have been very few real advances in years, as the Foundry guys put it did Darwin skip over email?
A big part of the problem is that email is a closed silo. Any tiny startup can crawl the web, try something different with the data and then show it to potential users. The barriers for mail are much higher, you either need to persuade people to migrate to an entirely new email account to use your service, or write a desktop app with all the overhead that entails. I've been heavily focused on finding chinks in the armor surrounding all the email silos, since I think that's the only way we're going to see real innovation.