Recently a news report came down indicating that a rugby player had tested positive for HGH through a new blood test. Up until this point, the main issue with implementation of blood testing was that it was not sufficiently reliable. By not having blood testing, HGH and other endurance enhancing options are undetectable (as far as we know).
News is now surfacing that Major League Baseball will implement such a test in the minor leagues, as a likely first step towards what would eventually be a major league level test. The NFL has recently proposed such blood-testing, but the NFL Players Association has come out adamantly against it:
"At this point, there's no reason to believe that blood-testing for NFL players will or should be implemented," said George Atallah, the union's assistant executive director of external affairs. "We should instead focus on preserving the drug-testing policy that we have in place."
In that Washington Post article there are some comments about what people think the usage rate is like in the NFL, with estimates ranging from 15 percent to 30 percent. There's no proof of anything one way or the other, but I in a sport like football with its low career length, I would think people would look for any edge they can get, particularly if it's undetectable.
As important as the revenue issues are in the current CBA negotiations, I would imagine this new blood test will be a fairly feisty issue and rather large bargaining chip.