I'm guessing I don't understand the email service, but if I assume it's separate from the current SMTP world, then...

• gmail is currently "good enough" most people wouldn't see 100% spam blocking as a big improvement

• no address for inbound email; can't post "my address" online

• friction to get the service set up, because an email client is included already on my machine, my phone, etc.

• might cost extra to be able to read my email anywhere (i.e. "cloud email storage")

Ok, so if it's so hard to replace email, how can it be done? Instinct tells me that until gmail loses some of its shine, nothing is going to happen. But gmail is more vulnerable than people think, and having a workable alternative when the time comes would go a long way toward getting people to switch. And if gmail fails, it's not going to be Yahoo Mail that steps up to fill in - gmail is the peak of traditional email services. I don't see how, from a technical standpoint, you could do any better than gmail without abandoning SMTP email altogether. (And I mean gmail along with all the accessory programs to make it perfect, i.e. iPhone integration, google apps for your domain, etc.)