Blues fans are long suffering, for sure. Over forty years of futility have drawn (as noticed on Twitter last night) lots of comparison with the Chicago Cubs. There's an important difference between the two teams, however: the Cubs have won the World Series. The Blues haven't gotten any further than runner-up. They're the Expos, not the Cubs.
But a few years of solid play, home-grown talent, good marketing, and pretty smart ownership has caused a buzz around the Blues, and it's grown. Forbes Magazine has compiled a list of the most loyal fans in the NHL, and the Blues have shot up those charts. The team's gone from being in 21st place in terms of loyalty to being tied with the mighty Pittsburgh Penguins for sixth.
Forbes isn't clear on how these are tabulated, but they do look at the following categories: pure entertainment (winning), authenticity (how well they play as a team), fan bonding, and history and tradition. The last one the Blues have done an outstanding job on with the Long Live the Note ad campaign. Fan bonding, well, the Blues hold many community outreach events and the like.
The Blues, like any team, gets bandwagon fans when they do well. That's taken into consideration. What's immeasurable here is the loyalty of the core, stubborn group of fans who follow the Blues through inconsistency, poor seasons, and the playoffs. You just can't measure that, and in my opinion, the Blues have one of the most loyal fan cores in the league.