I worked on a 100ft charter boat for the last 3 years or so and we had a procedure that we practiced regularly. Someone would toss a buoy over at random that had several large buckets attatched to it. This is from a crews perspective.
Whoever spots the MOB point and hollar and notify skipper/captain "man overboard, off the stbd/port side appx X meters back" (now everyone knows where MOB is). IMPORTANT, Never take your eye or pointer off the MOB as they are easy to lose sight of at night, rain, or waves. While doing this you and other crew must make sure no "brave souls" jump in after the MOB because then your problems have doubled. You or nearest person should then toss the throw ring, bag, or any float to the person. Then Confirm with the skipper/captain that they have a visual so they may plan the approach. Once the skipper/captain knows where the MOB is you may head to the planed boarding location of the particular vessel with your extended wisker pole and be ready to scood the MOB up.
Now I know the procedure would be different for a sailboat unless you decided to fire up the motor and drop sail, however the procedure of spotting, tossing floats, and notifying skipper/captain are very important as well as MAINTAING A VISUAL.
Sailingdog - its funny that you say MOB's are usually not able to assist because I had one captain that stressed how ugly it could get. He even said that if necessary we should knock them out so that they don't drag us in with them. I don't know about knocking someone out but people sure do get desperate in cold water.