Some lineage societies are quite well known such as the Daughters of the American Revolution (DAR), but the list of societies is extremely long, so a lot more people can be eligible to join than you might at first think. A good list of societies to use as a starting point is the Hereditary Society Blue Book - Societies on RootsWeb.com. Some links on this site are out of date, but I was generally able to find a web site for the society by doing a Google search. Some of the societies are by invitation only and others welcome open applications, so check each society's web site for details.
These societies often provide community service related to historical preservation, some publish educational magazines or newsletters, and others sponsor educational scholarships. Some scholarships offered were open to members and non-members alike. The range of benefits offered is unique to the organization and varies. The web sites in and of themselves are generally a great educational resource.
Another benefit specific to the genealogist is that many societies will provide you with lineage information on the qualifying ancestors. If you are experiencing a brick wall in your research, especially before 1850 when census lists did not list all household members, this may tumble you over the wall. Some societies will let you piggyback on this research if you are applying for membership, saving a lot of time and documentation as their sources have already been verified by other members, but again this varies by organization. All you have to do is then provide documentation to the point where your line meets theirs. If you don't actually wish to apply for membership, check out multiple web sites. Most have a list of qualifying ancestors printed on them and many have published books of their lineages that are available for sale or through local or history libraries.
This is by no means an all-inclusive list of the various benefits of lineage societies, but it is offered to give the reader food for thought. These societies are well worth pursuing as a potential resource to helping you past that brick wall ancestor.