I looked at the average height of NBA players, weighted by minutes played. For most of basketball history the players got bigger and bigger, but they peaked in the late 1980's. Since then the league has actually gotten smaller.
Starting with 1952, the average NBA player was 6'4. Four years later he was 6'5. In 1965, with Russell and Chamberlain dominating the game, the average player was 6'5.7. One more decade and the average topped 6'6 for the first time in 1976, and 6'7 in 1986. The average height stayed above 6'7 for just 3 years (1986-88), which is the time I was in high school. So you kids out there today, you didn't have to faced the kind of trees on your way to the rim that I did.
Since then the giants have become more rare. Average height fell to 6'6.5 in 2000, rebounded a bit, and then back to 6'6.5 in 2010. While there is a bit of year to year fluctuation, the average height has been within a half inch (6'6.5 and 6'7) for over 30 years now, 1981-2011.