One of the things I found interesting about Google's process was that everyone had input on their tracking system. Thus even when a person was a 'good fit' if there was someone in the company who had worked at the same company/time as the candidate, and suggested that the company pass, that carried a huge amount of force.

When ever I recommended someone I would check to see what the other folks that knew them added into the 'mix' if there was someone who clearly had an axe to grind (hey it happens) I'd try to talk to them one on one and figure out if it was a 'real' issue or just a past injustice that was motivating the down vote.

Sometimes it was warranted, there are good people who just don't fit with a company's culture. Sometimes it wasn't. One manager suggested that even if it was just sour grapes between the candidate and the employee it was a 'good signal' because the candidate burned their bridges willingly. (Although I'm a firm believer that people mature and change over time, not everyone subscribes to that philosophy either)

Be nice, be courteous, if they turn you down move on.