I saw a slide recently where the use of tablespaces was discouraged. What does the community think of tablespaces.
They are a tool and their use should neither be encouraged nor discouraged but rather understood and used when appropriate.
Their main problem to overcome when using them is that they tie PostgreSQL much more tightly to the underlying configuration of the operating system and thus you need to ensure that your processes and procedures accommodate that reality since the tools that PostgreSQL provides can only do so much.