Since this was put on the ATC section, I had to come and take a look <G>... In the US three miles is the standard in terminal airspace, and in certain conditions can go to two and a half on final. Of course if you are doing visuals, it is as close as the flight crew wants to do <G>...
As to enroute if you want five miles, true for the most part that is our minimum... But to set aside one arugument, the enroute washouts go to terminal not the other way around <BG>....
regards
Scott