What is the etiquete for unfriending people online?

In most online communities, it seems like there are those who are in it to make money or who have a very low signal to noise ratio. People with no real world bindings to me that became my friend for reasons unbeknown to me.

What is the proper etiquette for removing these people as online friends? Many sites allow you to flag a friend so that they are in your list, but you never see or hear from them unless they specifically target you. Facebook allows this handy feature. Twitter is a tool that doesn’t. You see all of your “friends” equally in your main feed with no way of filtering. At least it’s not possible from what I can see. Will these people become offended when some one else thinks they update too often? Is it worth wading through the noise in the hopes that through their ever expanding network, that they will link you to some one more inline with what you are looking for in an online friend? I wonder how much real world relations would change if you could remove a friend with a simple click of the mouse.