You probably don't want integer primary keys, and you probably don't want UUID primary keys. You probably want something in-between, depending on your use case. UUID is one extreme on this spectrum, which tries to solve all of the problems, including ones you might not have.
An example would be YouTube's video IDs. It's custom-fit for a purpose (security: no, avoiding the problem where people fish for auspicious YouTube video numbers or something: yes).
Another example would be a function that sorts the numbers 0 through 999 in a seemingly random order (but's actually deterministic), and then repeat that for each block of 1000 with a slight shift. Discourages casual numeric iteration but isn't as complex or cryptographically secure as UUID.
