One of the most visible areas of trademark use on the Internet is in domain names. Many companies register a domain name for every trademark they own, so that users of the associated products can easily find more information on it. However, when that domain name is owned by someone else, the company may miss those visitors. In the past, several people have registered domain names for other people's trademarks, in the hopes that they could sell those to the owners once those realized the importance of the Internet. Needless to say, few trademark owners were pleased by this, and some took action by suing the domain name owners for trademark misuse.
If you need to pick a name for your Website domain, ensure that it is sufficiently different from all other sites which offer similar services. Otherwise, you will cause confusion amongst visitors and you may expose yourself to lawsuits and conflicts with the owners of those other sites.
An interesting trick to get more visitors to your site, is to include the names of your competitors in a META keyword element. Search engines will then index your site and note that this name occurs on it. Users who then search on the word, will find your site and may go there in the hope it contains what they are searching for. Apart from the fact that many users will go away as soon as they realize they've been tricked, there is also the risk that the name is trademarked. In that case, the use in the META tag can be trademark infringement.
More information on patents, copyright, trademarks and other Internet-related law is available on Iusmentis.com.