First of all can I say that I did not think Crash & Burn's question was put in a bitchy way...and Bright-Ling, your reply to a posting that contains a legitimate question at the end does nothing to enhance the professional image of ATCOs - is the little 'knob' symbol at the end your signature?
Crash & Burn
No we are not required to seperate VFR and IFR traffic, but as pointed out the IFR can request traffic avoidance. Even then we do not have to provide standard separation (3miles/1000') we just have to miss them. However, in this day of 'Duty of Care' you will find more ATCOs practising 'defensive' controlling and providing traffic avoidance to the IFRs whether they ask for it or not. There is also a wonderful little phrase somewhere in our manual that says that VFR traffic should be instructed to avoid the areas where IFR traffic is letting down. Usually the easiest way of achieving this is with a quick vector (with the instruction of course to advise if unable to maintain VFR)
As for VFR/VFR all we have to provide is traffic information but even then it is very difficult to sit there and watch two aircraft steaming towards each other at the same level. No matter what the book says these days we live in a blame culture - I can just imagine standing there in front of the Coroner who is saying 'You mean to tell me you sat there in front of a serviceable radar and watched two aircraft collide but you did nothing to try and prevent it? Food for thought.