Re: ...Do you block people on MSN etc?...
Yes no one must be blocked on any communication medium.
It is not good to block some one. If someone bothers at times and is OK otherwise, this means that person is not good at least some time. So simply inform him/her and Block-Delete to end the story. No reason can be given to block some one. Any one who will find out about being-blocked will be hurt to some extent.