The safest assumption, as I used to tell my students, is that anything posted on the Internet may come back to bite you in the butt. You never know how long servers keep information, or how willing they are to turn it over if asked. The DOJ requests an incredible amount of information each year from ISP providers and other host servers. Some immediately comply, some balk and will ultimately prevail (or lose). The forensic capabilities of the DOJ, given the correct amount of motivation, exceeds the technical capabilities of most posters here. I don't generally subscribe to conspiracy theories but cybersecurity is a number one concern in the defense department and there is legislation pending as we type that will limit user's rights. PIPA is not dead, it's coming in the back door, through the Trans-Pacific trade agreement if nowhere else. ISP's, major utilities, and those with copyright and patent interests are all on board and have been actively participating in negotiations. A new govt facility in Utah is being constructed with a warehouse floor of servers dedicated to monitoring US network traffic. Stuxnet was a big hit on Iran. There are justifiable concerns that US could become a similar target.
That being said, one must keep in mind the risk, from the govt's point of view, one represents, as opposed to the amount of effort required and any benefit gained. Growing enough pot for individual supply, my guess, doesn't register on any radar screens. That doesn't imply that some discretion isn't sensible. Is "pot roast" a site administrator? Has anybody asked if rollitup has ever had their records requested, either in total or of individual users? They are not required to reveal if they have, but they will show up on the FOIA requests periodically I've seen reported, unless complying with FOIA is determined to represent threat to national security (though don't recall where can find reports at the moment)? Our personal rights are gradually being eroded in the name of the war on terrorism. I wouldn't assume the forum will protect anonymity. Going to court to fight requires money. Better to be a boring target and not post about having replaced your 5 acres of cornfields with a higher profit (more drought-resistant?) commodity.