it's all about relevance
The themes at Inbox seem to be relevance and heterogeneity. The attention and investment that's going into email -- at the ISP level, the enterprise level, the workgroup level and the client level -- signals that the channel isn't going away anytime soon. The folks here are focused on creating technology to improve the signal to noise ratio for the email user. Spam filtering, email collaboration tools, alerting technologies, client side developments -- they're all pointing towards helping individuals focus on information that matters to them.
This is not a challenge that's going to get addressed overnight, since by definition there's nothing more personal than "what matters to me." One filtering technology may solve your spam problem, but not mine. One email client may do wonders for your information management challenges, but fall completely flat for me. The application space is broad enough -- and the market is large enough -- to support heterogeneity of approaches up and down the delivery chain.