Normally I don't remove friends because I have been pretty choosy who to make a friend and I love them all. But I have unfriended few people for being from some other planet disguised as humans.
Mainly I only delete people that I rarely interact with anymore. There are a few that have not been on Lush in quite some time that I will never delete though, so i never forget them. One I know for sure is no longer with us and he was the first person I friended on here. One or two I still have the occasional contact with somewhere other than Lush, and some I just hope will turn up again some day.
I have a very short list. I like to correspond at times. Usually talking about writing or life in general. I will defriend when I am obviously being ignored.