Usenet (aka "News Groups") is one of the oldest and also one of the most useful parts of the Internet. The best way to think of it is as a worldwide bulletin board containing thousands of separate forums (known as "Groups"), sorted into a hierarchy of related subjects. It represents both the best and the worst that the Internet has to offer and can be regarded as a repository of pretty much all human knowledge - If you ask the right question in the right group you'll generally get an extremely knowledgeable answer within an hour or two. However, if you ask the wrong question in the wrong forum your mailbox will be full of insulting messages (known as "Flames") within thirty seconds...
Although most ISP's provide access to Usenet as standard, they usually restrict the number of groups available and generally provide a poor level of service in this area. To get the most out of Usenet you really need to subscribe to a separate, specialist provider.
One of the best Usenet providers is Usenet Monster and I can whole heartedly recommend their service to anyone looking to get the most from Usenet. The service they provide is quick, reliable and comprehensive with access to all of the most active news groups.
One of the most important aspects to consider when evaluating Usenet providers is Retention. This is the amount of time an article is available to be read once it has been posted, with a long retention period being better than a short one - especially if you don't have time to check your favourite groups everyday. This is an area where Usenet Monster really scores, providing an average of 14 days retention, so you don't need to worry about missing the conclusion of any interesting threads if you're unable to login for a few days.
Another nice feature of the Usenet Monster service is the concept of "Rollover Gigs", which means that if you don't download the maximum amount each month, any remaining gigabytes are rolled over into the next month. Very useful.
So, if you're looking to get the most out of Usenet, you really should consider Usenet Monster.