But many people rarely use their shell account, but still use the account for e-mail via a mail program on their desktop computer. Thus a person may still be checking mail daily but be registered as not having logged in for months. Plan files are a lost art. I think of plans as precursors to Web pages. They are text files that can be short or long, and give whatever information a person wishes to put there, whether it be office hours, witty quotes, etc.
Some machines only allow the plans to be read when someone is fingering from the same system.
The above are not links to a page at my site. Results should look similar no matter which finger method you use. Usually you finger someone with their e-mail address. Internet Helper by Andrew Cantino includes many protocols, including finger. Also has a finger server for serving files.