Further to ferris' reply:
In the UK at least, we still work on the requirement to use radar headings for separation. For example, if we have two aircraft head on or side by side and we need to climb or descend one through the other, we have to lock them on radar headings. Those headings will be selected at the time we decide to take the action, and will take no account of changing winds as the aircraft change level. More than a few people have been caught out by putting both aircraft on the same heading, only to find them drifting together as the wind takes effect.
Seeing as most common transport aircraft are FMS equipped today, it would be far easier and more reliable in terms of maintaining a track which will keep them apart if we could, for example, tell the aircraft to fly left or right by 3 miles from an airway centreline. Most FMS will maintain that far better than will a radar heading picked 10,000ft earlier. Provided we tell the aircraft not to deviate until advised and monitor it on radar I can't see the problem. Until such time, however, the scenarios described by ferris will continue to occur.