Honestly, skinning is probably easier today than it ever has been. With custom client-side stylesheets, there's no reason someone couldn't roll out custom skins for sites like Facebook, Twitter, etc.
Edit: I now realize that, taken out of context, my comment sounds pretty twisted.
The Web is a medium with built-in customizability.
This "our product is perfect and must be used as is" attitude reminds me of a relatively recent example that seems to be dying down: mobile websites that used the `maximum-scale=1 ` value in `<meta name="viewport"`. This disabled zooming in mobile devices. This was an accessibility issue that affected people who otherwise don't encounter other accessibility issues.
If it were simply a matter of providing the smallest payload to clients, these sites could provide some sort of external manifest/source map mapping human-readable class names to hashes.
Let's stop using divs for presentation whilst we're at it and spend man-years on picking the right semantically named elements with no benefit to anyone anywhere ever.
No ajax or js either, I'm pretty sure they didn't envisage that.
Edit: read the FAQ, downvotes are not for disagreement.
Commenting about downvotes in arguments isn't ok, though: https://news.ycombinator.com/newsguidelines.html.
Not to mention how your method could break tomorrow without warning because Facebook (or whatever you're skinning) push out an update that's incompatible with the theme you've hacked on to it.
Would also like to point out that customisation on MySpace is probably responsible for a whole generation of not only developers but non-tech focused people learning how to code. Met a lot of artists and designers who now work on the internet who MySpace was the starting point.
Not sure on the generation of web developers MySpace created. Pretty sure every single page that looked like this was plastered with logos for theme building sites/companies littered with various neon-on-black comic sans designs as far as the eye can see.
Anecdotal: I use a custom Facebook skin that makes the whole UI red and add a background image. Since I've started using it, I spend less time on the website. It feels, in a way, more tiring to use the custom theme.