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Think about it this way, if you are a user of technorati, would you be interested in your site? Would you click on an article and read it?

If yes, it's relevant, otherwise probably not, but even so I find it highly unlikely to affect you negatively.

It isn't very easy finding out the best performing keywords of a competitor, but how about searching for terms you think a visitor would find relevant, and seeing if your competitions shows up for it? Then search for variations on that.

When you create your own campaign, make sure you do phrase matching or exact matching, that's the only way to know how well a certain keywords performs, I've seen google send clicks for completely irrelevant searches for broad match which their algorithms thought was relevant.