As you probably know by now, the 2008-09 Caps became the 21st team in NHL history to win a playoff series after falling behind 3 games to one.
Of the 20 previous teams to accomplish this feat, fourteen were eliminated in the next round (in 2003, Minnesota defeated Vancouver, and each team had accomplished the comeback from 3-1 down in the previous round); and one lost in the Stanley Cup Finals (Vancouver, 1994).
The other four teams out of the 20 (i.e. 20%) won the Stanley Cup. Those four teams were:
-Toronto in 1942 (Winning the SCF after falling behind 3-1),
-Edmonton in 1990 (first round comeback),
-Pittsburgh in 1992 (first round comeback), and
-New Jersey in 2000 (conference finals comeback)