eWhisper.net reports that Google Adwords now enables you to exclude up to 20 IP addresses.
Sounds great but there are some concerns you should be aware of. Internet service providers tend to use a range of IP addresses for all their users. If you exclude an IP address of a competitor, you may be excluding hundreds if not thousands of potential customers on the same IP.
Before you exclude an IP, you can check to see if the IP is dedicated to one company by going to DomainTools and checking the url of the domain. You can then do a reverse IP (think reverse phone look-up) and DomainTools will indicate if there is one or one thousand web sites on the IP in question.