AdWordsAdvisor talks about the option of removing keywords with no clicks from your AdWords campaigns and its advantages.
[Link to quote
"I have many ad groups that have keyword with high impressions and no clicks. Should I remove those keywords so that my CTR will go up? I have tracked these keywords over the last 60 days."
So - IMO, when keywords have been around for 60 days, on a system on which tens of millions of searches happen every day, and they've gotten no clicks - the message that I get is that they're not real winners. And I can't really think of any real advantage in keeping them.
I'd also say the same thing for keywords that have been around awhile with no impressions.
On the other hand, there are advantages to getting rid of them. Just a few advantages, off the top of my head:
* less stuff to monitor
* makes it easier to monitor the keywords that remain
* may create room for keywords currently 'on hold' in your account
* our system will no longer 'budget' for them, which may make your other keywords show more often
* creates some 'head room' if you are near to a keyword limit for your account
And most important of all:
* gives you the warm fuzzy feeling of working to maintain AdWords system 'health', for the greater good of your fellow advertisers. And AWA. ;)