The only good explanation that I have for Ralph Nader's decision to enter the Presidential contest, collect a bunch of conservative money, marginally hurt Democrats from the left flank, and piss off most of his remaining natural allies is a need to be near the center of attention even when that attention is negative. Guess what Ralph --- you are irrelevant unless you are able to throw the election to McCain. There are not that many votes in the region that you want to inhabit, especially after your heighten the contradiction strategy worked in 2000 as most people did not believe that there was significant policy space between Bush and Gore. Iraq and healthcare are two obvious areas of significant difference this year.
I spent a couple of weeks during the summer of 2004 looking at Nader's signature petition forms to see if he qualified for the Pennsylvania general election ballot. I'll spend my August evenings this year doing the same thing. It's hardball as there is a significant policy difference on a couple areas of high personal salience to me and since we operate in a winner take all system, any third candidate hurts the major party candidate that they are ideologically closest to.