In our neck of the woods, in uncontrolled airspace we heavily rely on pilots making regular radio calls (position and intention reports). This has proven to work relatively well, at least outside the pattern. Away from the airfield, pilots tend to avoid reported traffic by a wide margin, and/or making arrangement with conflicting traffic to the same effect.
In the pattern the perceived restrictions in going higher or lower, or left or right, make people become more stubbornly stick to their planned trajectory. And then the lack of precision in reporting the exact position, combined with the lacking ability of most or all humans to create a perfect dynamic mental picture sometimes catches us out.
Thanks, Evalu8ter, and also echoed by many others here and in other threats. And who wants to disagree.
But it can also be the other way around. I just came back from a 1 hr flight in a busy weekend GA airspace. During the course of this flight, I made half a dozen of arrangements with other airspace users going to the same aerodrome that I intended flying over, or flying in opposite direction, to achieve or maintain 500 FT vertical separation, or similar. All based on blind radio calls, and thereafter both parties' mental determination that this might constitute "conflicting traffic".
To my total shame I must admit that despite my best endeavours I did not visually acquire a single of those other aircraft that I 'negotiated' with. We could as well all have been in a cloud, with the same satisfactory outcome. (Before somebody asks, I hold a recent Class 1 medical, and my - corrected - eye sight is well above 100%).
So how good would have been my chances to visually acquire traffic that I wasn't even aware of and expecting?