Last of the clients
I am seriously concerned that within a few years there will no longer be usable email clients available anymore. Certainly nothing that can also handle calendaring. Everybody is so hung up on using web browsers for everything, the talent and resources to develop purpose-built clients are rapidly dwindling. Certainly the Thunderbirrd-next folks are so busy with their yak-shaving that the client is going to become unusable before they even decide what colour they're going to make the menu-bar.
Browsers are handy tools for many things, email and calendars are not among them.