Heather,
Having previously worked for a company that had 4 dedicated trademark and copyright lawyers working in it's legal department (and working for me on web issues), it was our understanding that, currently, there is no protection for you in regards to people using "variations" of your trademarked name. It is understood that they cannot use your business name directly, which would come under the laws and statutes regarding Fraud. But they can get very close to mimicking you, without legal consequences coming into play.
If your company is ABC, Denver for example (officially registered with the state) and you have done interstate commerce, as well as owning and maintaining a web presence under abc.com, again having done interstate business, then you CAN go after people who use your name for any web site outside of your state. I only bring that up because two different businesses may have the same name in two different states. So you may find adwords and keywords in other parts of the US that are using "your" name.
You CANNOT (not until the laws change) stop them from using your companies name for ads, keywords etc., as your businesses name is a publicly used/displayed name. That is, Joe and his wife talk about ABC all the time on the street, using the companies name in conversation. Your company name is listed in directories, lists and maybe even on blogs that say deragotory things about you. You can't do anything about it - unless it is proven that the statements are blatant lies meant to harm your business.
In like fashion, others outside of your company have every right to use variations of your companies name for a new web site - one called ABCsucks.com (we bought several of those to keep them from the competition), for example, or any other derivitive of your name. If you don't want those names to be used, then you have to buy the domain names yourself to block them from being used. Been down that road for months with our lawyers - I know what I'm talking about!
What you CAN do, and many businesses underestimate the power of this concept, is simply hold to the high road, make your business and web site the very best it can be, and outshine everything else out there that would misuse your name. Even blogs or forums - if they say something bad about you, you cannot have it "erased" but you have every right to post a well thought out, balanced retort.
One company I know of in one city even contacted the competition and started a dialogue about taking the high road and asked if they could all agree not to use the other businesses name(s). They agreed and have not had that problem anymore.
Don't fret about sleezy practices on the web (liek the competition using your keywords) - it will eventually all come out in the open and lose it's bite. Just do your best to serve your customers, giving them absolute top notch service and respect, and all that other stuff really will diminish and become unimportant.
Hope that helps.