My colleague Tim Lee, blogging over at The Atlantic, raises the oft-repeated canard that Bob Barr's record on the USA PATRIOT Act is evidence of a longstanding unlibertarian track record, rendering his libertarian "conversion" suspect. What Lee and others fail to understand is that Congressman Barr was in fact the White House's chief legislative roadblock in their barreling PATRIOT through Congress. And that for his trouble, Barr earned the wrath of White House operatives like Karl Rove, which is what ultimately cast Barr from the Congress. (Thanks to Democrat gerrymandering in Georgia, Barr had to run against another incumbent Republican Congressman in the GOP primary, one who hadn't earned the ire of Rove's powerful machine.)
In 2001, Barr was the lead figure in the GOP-controlled House in pushing back against the PATRIOT Act, and ultimately suceeded in deleteing some text and forcing sunset clauses on the bill's worst provisions. Brad Jansen explains much of the background at American Spectator. More here. So when Barr started lobbying against PATRIOT Act abuses soon after leaving Congress, it was a continuation of his previous activities, not a reversal.
And those who remember politics before Bush may recall Bill Clinton's own "9/11", the Oklahoma City bombing. Just as after 9/11, a wish list of Justice Department powers was pulled off the shelf and given to the Congress to pass as an "anti-terror" bill. Freshman Congressman Barr then, too, cut back and limiited as much of the bill as he could from his seat on the Judiciary Committee. If you don't remember this from following the news at the time, you can read Barr's book and check his wikipedia entry for references.