If I lose track of time, it’s most likely because I was reading a website with huge numbers of pages all linked, which of course any wiki is a great example of. TV Tropes is probably the
worst best most time-consuming, but it can also happen with Wikipedia or other reference sites, or on any fandom wiki (of which TFwiki is by far the best in both completeness and style).
Basically, if there’s a subject I’m interested in and a ton of links, this can happen:
(xkcd also did one about TV Tropes, but I can’t remember its title.)
And more often then not, I’m there until I have an external reason to leave; not because I’m “done”.
It’s not entirely a bad thing since I’ve certainly learned things that I’ve been able to apply from some of those sites, but there are definitely times when I just look at a clock and wish I hadn’t spent so long there.