Outside of the whiteboard walls, which can be functional, most "start-up style" stuff is fluff. A nap room? Seriously? Are you employing pre-schoolers?
I'm quite a big fan of the Spolsky approach myself, especially for programmers. That is:
* everyone gets an office.
* high quality chairs (they don't have to be herman millers though, in fact, if you can afford it, let employees pick their own on the basis of comfort)
* external large format monitors, multiple if desired
* get everyone a laptop, it's nice to have a single computer, instead of 2-3
* an open area for collaboration (can in fact be a boardroom, but doesn't have to be)
* an open area for lunch/low intensity times (not the same as the collaborative space, and not filled with "cool things" like ping pong, but the spirit remains. Reading, eating and general socialization goes on here).
I'm not a big fan of putting non-work stuff like ping-pong and nerf guns into offices not because I don't want people to have a bit of fun, but because I think people should spend that time "the fun time" outside of the office with their colleagues, other friends or family.
It's a work environment, not a "life" environment.