And a lot of people report that the 2K crop introduces problems not present in the full sensor readout. Never tried it myself, so don't ask. But several respected rental andlens houses have warned me not to go that route.
http://www.youtube.com/watch?v=TIGN3XdWDUw
I can't find a Vimeo link, but this was shot by Matty_G, RED @ 2K, Zeiss S16s. It's a completely viable option... but, you have to pretty much to commit to it (like any other creative choice, though).