Even though I'm partial to most of Google's products services (Voice, Music, Picasa, Android, Maps, etc.) I prefer to use a "fat" email client (Thunderbird) to read/respond to email. My @gmail.com address is basically just a forwarding address to me.

My reasons for this don't really have anything to do with any sort of esoteric usage patterns, or being particularly scared of what Google is doing with my email, or any particular hatred for Google's mail functionality, rather, I just find native user interfaces to be far superior to web UIs. Navigating with h/j/k/l keys is understandable when you're running "vi" on a limited terminal, but the arrow keys exist for a reason, which is that h/j/k/l have other uses as, you know, letters in the alphabet that you'll occasionally want to type into a text field.

For this reason, computers over time have added modifier keys (in addition to "Shift") that allow you to signal to the application that you want to do some special action other than typing some text. We all make use of these every day in other applications -- including in our web browsers!

Of course, because "Alt", "Ctrl", "Command", "Option" and friends often have meanings to the application you're running, they're generally off limits to most web applications. You can catch special keys like arrows with JavaScript these days, along with Control keys, but generally you're very limited in how you can do keyboard shortcuts compared to what you can do in native applications. This leads to the awkwardness of having to pay attention to whether you have a text field focused in order to know whether you're going to activate a keyboard shortcut or type some text.

There are other UI niceties we've come to know and love on the desktop aren't available. Using Tab or Ctrl-tab to switch between panes, common in fat clients, doesn't work in web apps. Tabbed interfaces in web apps are awkward because you probably won't have access to Command-[1,2,3...] or Ctrl-[1,2,3...] to select tabs by number. Some web apps will have a shortcut key to focus the search field, but again, you're usually having to figure out if you're already in a text field to know if you can use it or not, when you could just Ctrl-F or Cmd-F in a normal desktop application.

I know these sound like nits, and to some extent, they are, because we all have nice pointing devices on our computers. Still, using the mouse to navigate can be a serious impedement to productivity compared to using the keyboard, and when you use a computer as much as many of us do every day and night, it really does add up.

AJAX and improvements to modern web browsers has made up much of the distance between the speed and functionality of native applications, but when it comes to usability, web apps are much further behind. Surely they'll catch up, but as of right now, I can't imagine having to use Hotmail 9.0 instead of a real email client.