I don't browse fullscreen.
Let me repeat that, in case it isn't absolutely clear. My internet browser is never maximized. I have a few windows sprinkled about my screen, the more the merrier, until I run out of space to put them. Thanks to you, web designers (but do continue reading even if you're not a web designer as I have a goodie for you at the end), this occurs as soon as I launch firefox.
But it's not your fault. I know how deeply you care about your audience. I know you are worried about the resolution of your website, that's why you gather statistics about our screen resolutions before exclaiming: "thank god nobody runs at 640x480 anymore, but I still need to cater to those poor saps who are still stuck with 800x600". So you build a website spanning those entire 800 pixels and I need to maximize my browser to see it and I get unhappy and I double my resolution, possibly buying a new screen to accommodate the change. And now your statistics tell you that even less people are stuck at 800x600 and you build an even wider website and I buy an even wider screen and I want to slap you silly for misunderstanding my contribution to your statistics.
Your assumption that your audience is browsing fullscreen is wrong. But assume for a moment that you realized your awful mistake and began measuring the size of the browser window instead of measuring the resolution of the screen. Then your statistics would still confirm that browsers are usually larger than what your site needs, and you will still greedily increase its size. This is because I came to your website looking for a piece of information, which I will continue to desire despite the size of your website. Your statistics will report the sizes at which your audience was reluctantly browsing your site, not the sizes at which they would prefer to browse it.
Now suppose that, in your infinite kindness, you decided to redesign your site so that it would scale automatically to fit each viewer's browser size. Would this make me happy at last? I would have hoped so, but most websites today do scale to fit my browser's size, and I'm still not happy.
The source of my annoyance is sidebars. Their width is usually small and fixed, leaving the bulk of the space to the actual contents. The problem here is that "small" is measured according to the web designer's standards, and the web designer is browsing fullscreen on a very large screen. This means that in my browser, those annoying sidebars will take up two thirds of the space and the contents will be so squished that I will need to resize my browser despite the website's struggling efforts to accommodate my size choices. At least when the websites had a fixed width I could scroll those sidebars out of the way.
Anyway, Gmail uses two sidebars, and I wrote a script to get rid of the right-hand one. That's the "goodie", "solution", constructive part of this rant.
The sidebar I'm removing contains mostly text ads, but that's not the reason I'm removing it. In fact, if you came here looking for a way to remove those adds, I'd advise you not to. Well, sure, go ahead and remove the ads if they bother you, but if the sidebar doesn't bother you as well then don't get rid of an entire bar just to get rid of a few ads. The sidebar does contain a few useful things; I've never used its "New window", "Print all", nor "Expand all" buttons, but the bar does occasionally contain golden suggestions. It once parsed the text of the message I was reading, discovered that it was an invitation, and provided me with a button to add the event to my calendar. It even got the time, place, and event description right! I bet that Google will find more cool ways to understand our messages and provide us with smart buttons, but I'll miss out on them if I remove this sidebar. Oh well, I guess my hatred is greater than my enthusiasm.
Here is the script: wider gmail. It's a bookmarklet, so don't bother clicking on it now, it won't lead you anywhere. But if you put it in your toolbar, and click it once you're in Gmail's conversation mode, it will toggle the right-hand sidebar on and off. And if you'd rather have the bar hiden by default, here is a Greasemonkey script which should do the trick.