Much wailing & vitriol emanates from liberals in the US over Ralph Nader's decision to enter the Presidential race (http://thecaucusblogs.nytimes.com/2008/02/24/nader-to-run-again/ ).
It's taken as fact that Nader's candidacy in 2000 robbed Gore of the election. Ridiculous. Quite apart from the shennanigans in Florida, where Dubya's brother, as Governor, fixed the vote in that state, the reality is that Gore simply couldn't convince enough voters that he had what it took.
Backers of Barack Obama will spin the line to the media that Nader is a spoiler, even a fifth columnist. Such is their vacuous stance; Obama's speeches are replete with platitudes, truisms & feel-good rhetoric. He is policy-lite & personality-laden. He is a more progressive candidate than Hillary Clinton, but that's not saying much.
Nader represents a large proportion of US voters who are continually frustrated that their philosophy & economic stance is dismissed by the Democrats as dangerously left-wing. He has every right to stand.