Harris writes: I'm working on a one-hour spec pilot that thematically and tonally feels suited for premium cable. Should I be including traditional act breaks and such?
Great question. I say no. Anyone with other experience can feel free to comment, but when I wrote my Weeds spec I studied several real scripts and found no act breaks, so I copied that format. After a look at the Pilot School website, I found that The Sopranos is the same.
HOWEVER - and this is a big however - I'm talking about format, i.e., actually writing "END OF ACT TWO" - not structure. Premium cable doesn't give you a free pass to ignore structure. While you might not need traditional cliffhangery act breaks, you still need story turns. I thought of my Weeds in a beginning-middle-end-tag fashion: the problem, what we do about the problem, the ramifications of our choices, and the set-up for next episode's problem. Watch episodes of other premium cable shows and see how they do it. Many of these writers have also written for network or basic cable, and I bet already have traditional structure ingrained in their minds.
UPDATE: Okay, you guys have convinced me. In the interest of using your spec pilot as a sample for a variety of shows, put act breaks in your pilot. But don't put them in a spec of a show that doesn't use them.