I am actually quite surprised by many of the views posted in this thread. I think many are extremely naive and others are seemingly defiant for no apparent or logical reason.
Vbham is absolutely correct regardless of how anyone may want to spin it... at this point voting for anyone other than Obama or Romney is in fact supporting the candidate you would least want elected. If you favor one over the other, even if only slightly, then you should vote for him. If you clearly do not favor one over the other then you should just stay home and make the lines shorter for those of us who want our vote to count.
Anyone who thinks they are "sending a message" by voting third party needs a major dose of reality. Other than how it may affect them (which was I believe the OP's message), neither party cares if you decide to vote 3P or not vote at all. To both Dems and Pubs the end result is the same... it's either a vote they didn't get or their competition didn't get.
Now... I am very much in favor of a 3P rising up and hopefully waking up both the Dems and Pubs because they each need a major slap in the face. Unlike some, however, I think it is quite possible for this to happen and at some point (if things don't change) likely will happen. There have clearly been opportunities in the past when a 3P could have become a significant factor in a major election. You only need to look back as far as the creation of the Tea Party. Relatively speaking, they quickly rose to prominence. However, they never really delivered a key figure head that others could rally behind which seems to be the reoccurring failure of most third party movements. Michelle Bachmann??? Seriously??? How about Jesse Ventura... really???
If a Christie or Rubio were the figure heads for a 3P movement you would see a MAJOR swing in viability. When this happens, then we will see the rise of a third party.