I'll start by saying something you already know: the Caps are the best team in the NHL so far this season (note the goal differential). Now for something you may not know: our overall awesomeness has hidden that fact that our powerplay is historically good.
Nerds like me know that this team was carried by the powerplay last season, having a +27 goal differential in the regular season, with 10 of those 27 goals coming from special teams differential between power play goals for and short-handed goals against. We also were on the powerplay 50 fewer times than we were shorthanded last season. In short, the Caps of 2008-2009 were a good team that was elevated to the upper echelon of the NHL by an elite powerplay.
This year, the 5-on-5 has gotten better, and so has the powerplay. We currently have a +80 goal differential overall, 25 goals better than the next-best team, Chicago. Of that 80 goal differential, 14 of it has come from special teams. Last year, our PP ranked second in the league, behind the Red Wings, but this year, we have taken a huge step forward. Sure, our 25.9% powerplay percentage is almost identical to last year's, but we have the best raw powerplay scoring rate since the 1995-1996 season. That's right, we have the best powerplay scoring rate in the last 15 years! Not only are we scoring at a higher rate than any other team in the past 15 years with the man advantage, but we are 2.6 percentage points above the next-best PP team. That 2.6% may not seem significant, but is tied for the largest gap between the top-2 powerplay teams in the league with the 2002-2003 Red Wings during that same 15 year span.
Going even further, I ran the numbers to compare these two powerplays to the league average. This season, the league average powerplay scoring rate is 18.5%, which puts the Caps 7.4% over the league average. In 2002-2003, the league powerplay scoring average was 16.4% and the Red Wings were at 23.8%, which is also 7.4% above league average. Relative to the league, this leaves the 2002-2003 Red Wings powerplay as slightly better than the 2009-2010 Caps edition (44% above league avg. and the Caps are only 40% above league average). As a comparison, the team with the next-best differential above the 2nd-best powerplay in the past 12 years is the 2007-2008 Canadians, who scored on 24.1% of their opportunities, were 2.3% above the next-best team, 6.4% above the league average rate of 17.7%, and 36% better than the league average. Those numbers are very good, but this year's Caps and the '02-'03 Red Wings have been the 2 best powerplays of, at least, the past 12 years.
You will not see the Caps on any list of historically great powerplays thanks to the higher scoring times of the NHL and lack of parity back in the 70's, but this year's team has a strong case as the best powerplay in modern NHL history and thus as one of the best of all-time.
(Research courtesy of espon.com and nhl.com, and image courtesy of causewaycrew.files.wordpress.com)