TwitterSnooze allows you to put someone (or a bunch of people) on hold. Instead of unfollowing them, you simply make it so you do not get their tweets for a specified period of time.

This may be useful if the people you are following are all at a conference that you are not very interested in. Apart from that, I really do not see any other uses for it.

Two problems with it, however. While you have a person on snooze, the server will store your Twitter password. A lot of people are not happy with this. The other problem is that when you take a person off snooze, they get a note telling them that you have taken them off snooze.  To deal with this, the people at TwitterSnooze have a card you can send to the person.