> Do I need UUIDs? Maybe not, but after much debt, I've decided that the storage requirements of such an index in memory is worth the ability to move from Postgres to Postgresql-xl.

There is a major benefit to UUIDs besides server-side scaling concerns: you can generate them offline in mobile apps and other client-side applications.

With serial primary keys, you are often stuck between waiting for a server round trip before saving data locally, or inventing complicated solutions for referring to not-yet-uploaded data locally.