Well I think 404 is only the first problem you have to solve and people don't even do that very well, then declare success and move on. I've seen so many developers try to reinvent things that are in the HTTP 1.0 specification.

I've definitely had to deal with problems of people returning 200 not found and those leaking up into higher layers of the system, and I agree with the people who don't like that solution. 204 is probably better, but I've seen too much code that looks for 200<=status<300 so you're still dealing with the same problem, but at least that's a client bug not a roll your own thing issue.

On one project, I put the kibosh on someone trying to negotiate clock skew detection between the client and server. I don't recall what they were going to do about it but I pointed out that information is already in the request headers, and has been from the start. So if your timing decisions are tied to an HTTP request, you don't need to do anything out of band to negotiate a common notion of time.

I don't recall when I stopped seeing timestamps of January 2, 1970, but I know I saw enough of them that it stopped being a novelty and I stopped looking for them. In 1995 when they were still working on the spec, nobody used NTP yet, and many, many people had a dead or dying CR2032 battery on their motherboard and either hadn't noticed or didn't know where to buy a replacement. The dying ones were the worst because sometimes they would hold the time but not increment it properly, so the clock skew was proportional to how many hours a day they turned the machine off. "Expires on March 1" didn't mean anything, unless you knew that the server thought it was February 28th. I suspect Tim was thinking of time zones between scientists in Switzerland, France, England and Germany, but it worked really well for crap hardware too.