At Under the Dome Ryan points out that Bob Barr received more votes than Barack Obama's margin of victory over John McCain in North Carolina and declares him to have been a spoiler.
I guess it depends on how you define spoiler. Merriam Webster says 'one (as a political candidate) having little or no chance of winning but capable of depriving a rival of success.'
Did Bob Barr cost John McCain North Carolina? I don't think so. Barr got about 26,000 votes. Obama won by about 14,000 votes. McCain would have had to win the Barr voters about 77-23 to make up his margin relative to Obama.
An analysis we did in early October found that Barr supporters were voting for Democrats and Republicans almost evenly in races for offices like Governor and Senate. And as a commenter on that thread pointed out, a lot of Libertarian voters may just not have come out at all if their only choices had been the major party candidates.
On the list of reasons why Barack Obama won North Carolina I think you can put Bob Barr's presence on the ballot at about #468.