Yeah, there are a couple of people from Pivotal working on a column store right now, but a major limitation is that while the storage is now pluggable the query planner and the executor still assume all engines are row based which prevents PostgreSQL from taking full advantage of a column store.

Edit: Another project for a new storage engine is zheap which is a new row based storage which uses undo log rather than storing multiple row versions to reduce the amount of bloat.