"...is my friend" according to the saying. I seem to remember a humourous extension of FOAF aiming for this territory a while ago, which sparked my interest. The problem with the above-saying is that it is a paradox in certain critical situations where trust is involved. I don't want to be overly political in sensitive times, but the relation of the USA to Iraq and Iran (implementing this strategy) over the past three decades is a case in point.
Map out the relationships - Iran and Iraq have been reciprocal "enemies" during this time, so let's assume the US takes up an antagonistic approach to Iraq, then the eneny of its enemy is Iran, its "friend". If the US then gets fed up with Iran and takes up an antagonistic stance towards it, by this strategy, it is honour-bound to do a volte-face and make the enemy of its new enemy its "friend" i.e. in this case Iraq. I don't think it takes a genius to work out the drawbacks of this strategy - there are numerous instances of this happening with the foreign policy of various governments, and the Iran/Iraq issues are still rattling on.
Anyway, getting back to my sheep, my point was that it is a risky strategy to suggest anything other than predisposition towards a relationship in a social network unless that relationship is directly stated. I know that my above example does not map directly to the virtual world, but I still think it's an interesting bone of contention.