[something123]

To the first point, I think this might be controversial... but try to avoid people you work with directly. It seems like it's better at first glance - b/c you interact with them more - but the reality is there are whole layers of professionalism and competing interests between you and them which actually kinda preclude you from building a system of mutual trust.

Maybe "trust" isn't quite the right word, but I'm struggling to find a better one. The difference between an acquaintance and a friend is that you can implicitly know they will help you and that you will help them. This involves being willing to do thing while expecting nothing in return. In a work setting that usually leads to bitterness

But that's just like my opinion man...

[TrevorJ]

It's pretty situation dependant. Mostly depends on the corporate structure, culture and your positions relative to each other. I've been blessed to work at small companies where most of the people I rub shoulders with aren't in the same professional 'track' as me, so there's no real reason for anyone to use a friendship to jockey for position or something.

[bbcbasic]

This seems right to me in general, although there has been exceptions in my case. I think for better or worse alcohol can be the social catalyst that knocks down those barriers. But yes in general there are competing interests and people have their guards up. I think ex-colleagues can become good friends more easily.