I can't figure out what the rules are on using brand names as keywords in a campaign. From what I can pull up, there is a difference between using a brand name in the actual text vs. just bidding on the keyword. To put it in perspective, I'm seeing no ads when I google "Ebay" or "Facebook", or "MySpace". Also, usually when I google "Twitter" I see zero ads, but every now and then there is one or two. What's the deal with bidding on brand names if you don't use it in the ad text itself?