In my opinion, it's very much dependent on what the thread is. Like Ezra and jrjones said, bumping personal threads from long ago isn't at all helpful, and it's extremely rude when it is done to ask some philosophical question.
However, it can be good to resurrect helpful threads from long ago - GAD is often filled with topics which have been covered several times in the past, which gets annoying when you've been here since July 2012.
I do object to people being hostile to new people who necro-post. People who come here may be new to the concept of forums, as I was when I first signed up under my old account almost two years ago. It is somewhat frustrating, but is it really so difficult to give a friendly explanation?