A rant on web design:
A lot of designers treat their sites as, essentially, artwork—
their artwork, with emphasis on the possessive. They get to choose how it's supposed to look, how you're supposed to navigate through it, and what you're supposed to use it for. They're fully entitled to change colors and fonts and font sizes. And they get annoyed when people mess with their precious art. This is the attitude that causes people to do things like try to find ways to block your browsers' preference settings on layout and font, or to use

to make it look like they intended it to.
I think the following comment (found in an article about Gmail blocking browsers with Greasemonkey installed) sums up this attitude quite well:
Personally I dont think greasemonkey is right anyway [...] from googles point of view, youre basically hacking their site and making it do things it wasn't intended to do. I wouldn't want people messing with my sites either. (sic)
All right, web designers, listen closely:
this attitude is wrong.Web pages, in the main, aren't artwork. They serve a purpose other than being visually appealing/moving/whatever. They exist to provide information or a capability or a service. Expedia isn't there for me to admire; it's there for me to make plane tickets from. And my ability to adjust that experience makes the web page
more able to provide functionality to me as a client, not less.
Print media are pretty much fixed. When you're doing a layout for a newspaper, it's going to go to print the way it is, and it will either work or it won't. It makes sense to think hard about the visual presentation, and do the best you can to make it appealing and accessible to the largest number of people. But if you could have a newspaper that automatically adjusted itself to use a larger font for the 10% of people with weak eyes, would you tell those people "Your preferences are wrong, I'm sure it's better with the smaller font?" Would you deliberately adjust the layout on an ad to put the text at the bottom, knowing your target audience was looking for it at the top? Well... maybe you would, I dunno. But you shouldn't. And that's exactly what you're doing when you try to set your web page in stone.
I've just quit using Expedia, which I like, for one reason only: they've changed their web layout to pin down the placement of some tabs, and now critical links end up behind those tabs when a larger font is used. Okay, the tabs now stay where the designer thought they looked best. But trying to access my most recent itinerary brought me quite literally to tears of frustration—I ended up grubbing through page source, just trying to figure out how to get to my damn flight. And that's stupid.
Yes, it can go too far. You can change a site so much that it's offering services you don't want to provide (such as
using your gmail account as an external hard drive). But if a user wants to add a more intuitive way of deleting a message,
let them. You should be thrilled that they like your site enough to try to individualize it. And you should look very closely at how many people agree that certain changes are worth making.
Browser preferences, bookmarklets, and tools like Greasemonkey offer the web designer an unparalleled opportunity to give their consumers exactly what they want, at no additional cost. All you have to do is not deliberately screw it up. It's not hard; it's what the web is designed for, after all.
End rant.