Pilot Pete,
Good post. I've met lots of wannabees (and spend a lot of time browsing here looking for snippets that may lead to an opening) and I'm always surprised and disappointed by the number that would sell their own grandmothers to get a position, let alone stab a friend in the back on the way.
I think that is a pity. My frist break came from some info a good friend put my way, and I have never hesitated to do the same for others that I meet. I take the view that one day, should they find themselves in a position to help, that they will seek to do a friend a favour over some stranger they've never met. I'm happy to share information with my friends regarding contacts and opportunities, as if I am unsuccessful I would consider it the next best thing to have a friend land the job instead.
On the subject of using friends to get some inside assistance, I wouldn't seek to do that unless I had discussed it first, and they were happy to talk in positive terms about you. There is nothing worse than having somebody approach you seeking an informal appraisal of an aquaintance who you think is a muppet, but who is obviously hoping that you will say nice things about them. It can be mutually embarassing when they subsequently fall flat on their face, or otherwise disgrace themselves.