Microsoft announced that they now are allowing advertisers to use the negative keywords feature at the campaign level. This way, you can apply a negative keyword to all the ad groups within the campaign, as opposed to adding the negative keyword to each and every ad group.
To add negative keywords at the campaign level for a new campaign:
1. Click the Campaigns tab. 2. Click Create campaign. 3. In the Name text box, type the name of the new campaign. 4. To add negative keywords to your campaign, first click Advanced options, and then in the text box, type the negative keywords (separated by commas).
More details at the adCenter Blog.