I’m with Dick on this one: ideal office space for a startup is a big fishbowl with no/few offices. Read Dick’s post for the benefits; I largely agree with everything he says.
For what it’s worth, Overture used to be the-whole-floor-is-one-big-open-space-with-no-cubicles, so it can be scaled to much larger than 30 people (each floor was probably 100 people). Not that everybody liked it - in fact, many disliked it.
My favorite workspaces: the lab at Scripps C4, which was a bunch of workstations in a large U shape with shared private offices for taking phone calls / naps, and our first space at Binary Evolution, which was a wonderful 500 square foot no-windows former sweat-shop (literally) next to a porn shop. I was probably the only person that like that space though.