Bulgaria didn't have as high a standard of living as Romania at the time, 2009, but Botosani county on Romania's Moldovan border was the poorest county in the EU. Whether or not it still is, I do not now.
The argument has been that by specifying what each URL part is, you can build a link to https://pinboard.in/t:minimalism in the first place. Is delicious.com/minimalism the tag minimalism or the user minimalism? And what is delicious.com/settings? In practice, delicious gets around this by making all-user tags accessible at http://delicious.com/tag/iphone, but then you can't have a user named "tag". Or "tools", or "help", or "about", or "terms", and there's probably more and they might change every now and then.
As a long time pinboard user, I devoutly hope not. It's a great service for antisocial people like me, and I'd be disappointed were it to develop that "social" layer of oily mucus.
You can already subscribe to tags. It's not social in a sense that you can interact directly with others, but it does have a secret feature of sharing your bookmarks with others by making them public.