[deathanatos]

> Not sortable

That's not correct; its trivial to come up with an ordering, and I don't know of a database in practice that doesn't permit sorting on a UUID.

> Table relationships are annoying

… in SQL,

  user_id REFERENCES users

It's exactly the same, regardless of the type of the column…?

> Takes a lot of space

Yes … but also no. It's 16 B vs. a serial's 4 B, I grant, but compared to a varchar, it's immaterial. (And particular in comparison to the number of times I see people use a varchar for an enum…) Certainly there could be a case where a row is wide b/c of UUIDs, but in practice, rows are wide either because of the data, or because of poor design.