I think you if write an email or type specific keyword in instant messages or participate in a forum or whatever and those words contain keywords they are going to be read by NSA.
Say you type: bomb new york
In fact this post will be read by the relevant authority.
At least according to Dan brown's digital fortress
.
But the guy is credible and if he's not it's the govt making him look so.
But to participate in a terrorist related site before actually wanting to do a terrorist act is just plain stupid. Those sites must have gotten a personal attention by the authorities.