In facebook you can set it so that you see less of someone’s status updates. Useful because you don’t have to remove them as a friend, but you might still see some updates.
In Twitter you can’t not see someone unless you remove them. But you might not want to do that.

In Socialthing there is a grey bar with the person’s name. On the right of that you can choose a colour and next to that is an arrow. Clicking that lets you remove the person from your socialthing view. Neat.