The HSTORE extension has been around quite a while, but until recently I've never found a situation where I can justify using it - here's a quick writeup of a simple use-case.
The application which runs this website is a homebrew one which I've been maintaining on-and-off for over a decade, initially so I could have a Perl'n'PostgreSQL-powered website which provided some functionality not otherwise available at the time; but also as a platform for experimenting with various database and web technologies. As such the underlying database schema has suffered some sprawl over the years, and recently I've been tidying things up.
One source of the sprawl are a couple of key/value tables I've created at some point to store arbitrary attributes to associate with records in other tables. For example, this application is basically a CMS which runs multiple sites from the same database; it has (and who'd've thought it) a table called " site ", and associated with each site are a number of ad-hoc options which I've added as I've needed them. The table isn't very large and basically looks like this: