Don't assume that users of your applications know too much about how to use it. With every new application, users pass through a learning phase that can be painful sometimes, especially if your application usability was not tested by an average user.

However, there is an assumption that you can always make about your users: they know how to use email. If your application looks a lot like an email client, you can be confident that users won't have usability problems with it.

I tried to mimic a mail client a lot while designing the administration interface of the sfBlogs application. I know of two other applications that follow exactly the same path:

MarsEdit is an OSX only application to edit and post content to your blogs. It's snappy, easy to use, and it looks just like Mail, Apple's default mail client on the Mac. If you're tired of the browser, MarsEdit is a great way to edit your blog offline with a familiar interface.

Multiply is a media sharing web application designed to "make it easy to create, share and discuss your blog, photos, and videos with more of the people you know, and fewer of the people you don't." It looks just like what sfBlogs would be if I had enough time and skill.

If you wonder how to design your next web application, think about a mail client. It might save you months of usability mistakes.