I'd have to say that Self Control is probably the only useful one for me. If an IM pops up or I have an urge to browse HN, I'd circumvent any of the apps that just dims other apps if I want. And for the Pomodoro timers it's too easy to deviate off schedule, and too many tasks that are too short to time.

Self control however is ingenious. I can impulsively block sites, only to block impulses to visit sites afterwards.

That reminds me though, I seriously have to start using the procrastination feature here at HN.