A few people have already used "Web 0.5" by back-construction from Web 2.0. Sean Coates used it derogatively of MySpace, but this O'Reilly blog post is more positive, suggesting Web 2.0 is a return to earlier Internet applications.
But if Web 2.0 was about interactivity and collaboration in a community context, Web 0.5 should have less of those - while still being part of the Web. So I prefer to use the term for web sites that don't support comments or other interaction, aren't dynamic, and could have existed in 1993 (a decade before the Web 2.0 conference).
I don't see this as negative - just as print books and ebooks coexist, there's no reason for web sites to all be embedded in social networks.
My own web sites are largely Web 0.5, though not as purely as a site like the Complete Review. This blog is the most modern of them, since it comes with the full WordPress apparatus of comments, trackbacks, RSS feeds, etc. And even the static sites have CSS, some "post to" links for social media sites, the odd RSS feed, and the occasional bit of Javascript. (I've been known to joke that the Web went downhill when they added graphics support and my largest site, the book reviews, is unusual in having no images.)
Update: if your browser supports it, take a look at Welcome to the web 0.5
I don't think there's any javascript on my site. We got comfortable with trn for reading usenet, and then (text-only) lynx for the early web. So there's a distinct inescapable nostalgia for that speed and elegance.
Yes, speed was (and I would argue is) definitely part of the Web 0.5 experience! Even on the other end of a 9600 baud modem, lynx was zippier to use on pretty much any 1993 web site than Firefox is over broadband on a lot of modern sites that are stuffed with Javascript and video.
The more powerful our tools get, the slower they run!?!
I'd reference "feature creep" here to explain it. That is when future versions of software (and other things) have more features you don't want and become more unreliable and slower because of it. That happens because people keep trying to make it do more things other than the specific thing it was initially designed to be good at.
It's not as certain as entropy but it is comparable.
Is there an explicit design philosophy about how to avoid this slowing/creep/bloat? Like a browser that shows a lynx-style text-only page while the fancy page loads? "New Twitter" is a disgrace!
I don't have a good answer for you; if I were a more rabid *nix developer you asking that where I might respond is comparable to inviting me to preach about the virtues of the console and compiling your own operating system.
The closest I have to a good answer is to throw out inadequately performing solutions and get rid of legacy issues with adequate regularity. All sane open source developers understand there is an end-of-life to any project.
To deal specifically with Twitter I'd suggest looking for third-party software to fix it. I don't touch Twitter but I'd be surprised if there are no Firefox extensions or something.
I am a big fan of these mostly-text layouts. I am interested in content, not noise.
For an amusing rant about the modern web, and especially CSS and Javascript, I recommend James Mickens' "To Wash It All Away".
Web 0.5 would be perfect for Minix 3 users, it comes with a choice of Links or Lynx as your browser.