Gmail is a great mail interface. I prefer it in many ways to even outlook. There are basically two deficiencies it suffers from currently. One big and complex the other is low hanging fruit that Google should pick today, Shared Folders. I should be able to share a virtual folder with another Gmail user. I would only need to know their gmail username to set it up.
There’s the fruit G-Buddy, now go pick it and let the users go wild.
The other need is a calendaring 2.0 app that is open enough that I can write sync utilities for my phone/palm/pda/etc. Now that is one big honk’in project. I’m confident that some very bright minds are working on it as I type — but we want sharing there too. Also, I assume that they’ll be using vcal and the rest of the standards.