Both sites were founded around 15 years ago.
But they're both still going. (GoodReads, of course, now being owned by Amazon.)
Which seems like a pretty unusual situation to me -- can't think of too many parallels where the extreme underdog doesn't either a) just call it quits or b) keeps innovating until they get some kind of "reasonable" market share, whether that's 10% or 30% or 50% or 80%.
Above all in a social network. (A big value of GoodReads for me is seeing my friend's books and activity too. As much as I'd be curious to try LibraryThing, I don't think any of my friends have even heard of it.)
I'm quite curious how LibraryThing has managed to keep going despite such a tiny userbase, comparatively? I'm genuinely impressed.