Facebook Poke features can be used for various things. For example, you can poke your friends to say hello. When you poke someone, they will receive poke alert at their home page.
Poke feature is intended to attract the attention of another user. Many Facebook users use this feature to attract attention or say "hello" to their friends.
Maybe there are some applications on Facebook that have the same idea with the poke feature. Some people consider it disturbing, others regard it as a form of the game, and still others just use it to waking up their friends to start posting updates again.
I think the general purpose of this feature was to say "hi" to your friends and let them know that you (are) on Facebook. What do you think?