The easiest thing to do when you are bored that comes to my mind at the moment is to type “bored” in Google. Searching for the keyword “bored” will list over 60 million results. A lot of the sites tell you what to do when you are bored, and I think that it is almost impossible to be bored when you have access to the Internet. There are simply so many things that will entertain you for many hours.
If you are a social person who likes to talk, then you can take advantage of numerous chats or social networks available on the Web. There are millions of registered users on sites like MySpace, so you should be able to find like-minded people that share your interests. There are also some websites that allow you to talk with characters having artificial intelligence.
If you are looking for a challenge, then there are plenty of arcade games and puzzle games that you can always play. Many of them do not even require you to download anything. If you like to both interact with people and compete with them, then you can take part in one of the many virtual worlds created on the Internet. There are a lot of possibilities on the Internet, and I am sure that you will find something for yourself.