2009-07-06: Abuse it and lose it
You will lose the rights to give user reputation if it's apparent that your main use of the reputation system is to make petty comments because you have a grudge against a particular user.
Likewise, you will lose the right to tag posts should it become apparent that you're adding pointless tags to a thread. The system is to aid the findability of content, not for filling with the clutter of cheap gags or snipes.
It is worth noting that the majority of people have nothing to worry about in using the above features of the forum. It's the minority who are spoiling the party, and those people know who they are and should not be surprised in the slightest to find they cannot give reputation or leave tags.