About a month ago I re-discovered that you can actually run email client on desktop and unexpectedly liked it. That is odd - I distinctly remember some kind of pain associated with this activity in the recent past, so I tried to sort this out. Mainly for myself, but may be someone else will find this useful or amusing. Desktop client I'm talking about is Windows Live Mail. It is free and light weight, generally you install it with new OS as part of Essentials package.
It runs in the browser which, in today's world, means you only need a computer to get to it. You can access it from anywhere at any time because, as Google tells us, browser is modern day OS. It does not require additional software installed and most web UIs in usability and functionality very close to their desktop counterparts.
Depending on your email provider(s), experience can vary. You might have annoying adds, sluggish performance, ugly and confusing UI and, if you have several accounts with different providers, you need to jump between them or get yet another web service to consolidate them together. Offline feature, if at all available, not always pleasant.
Desktop apps still feel faster and more robust than apps in-the-browser. You can add virtually any email account to Live mail and get consistent solid interface to all of your mail. It is add free, fast, reliable and easy to use. As a lot of people I have at least half a dozen accounts and having them all in one place with ease is very important. It used to be a pain to configure them, going through help to get SMTP and POP servers, port numbers etc. but Live mail does outstanding job finding this out for you. I just have to give it my email and password and got "ready to use" message almost instantly. And it isn't just Gmail I'm talking about, it got a lot smarter from last time I used Outlook. And, naturally, it handles offline mode with no sweat.
If you want to quickly check email on your friend's computer - you'll have to drop back to web mail, so you still kind of sitting between two chairs.
It is fascinating to see this blurring line between desktop and web. For now, I decided to use Live Mail for all my email accounts, including Gmail - because at the moment it works best for my needs. That would be super cool if MS included Live mail as default email application for Windows, so you can just click an envelope icon and, if you at someone else's computer, click "guest" button, type in your email/password and get messages loaded. Preferably with tasks, calendars etc. Yes, I remember Outlook Express, but it was half-baked freebie to get you tricked into buying Office with "real" Outlook. Live mail just in the totally different category - no one in the right mind would want to replace it with that overweight dinosaur from the corporate zoo.