I have always been a big proponent of taking RB/RB with my first two picks, but that train of thought may no longer be wise. Here's some trends that can't be ignored.
from ESPN Researcher Jason Vida:
Last season, the player who led his team in rushing attempts accounted for fewer than 54 percent of his team's attempts, the lowest percentage in the past 10 NFL seasons. At the same time, a team's second-leading ball carrier (the player with the second-most rushing attempts on a team) got the ball on more than 23 percent of team rushing attempts, the highest percentage in the past 10 NFL seasons. The bottom line: In 2007, NFL teams gave fewer carries to their leading rusher and more carries to their second backfield option than in any of the past 10 seasons.
Futhermore, only three running backs averaged 20 carries a game last year (Willie Parker, Clinton Portis and Edgerrin James). In the previous four years, at least seven runners got at least 20 carries a game.
Meanwhile, in 2007, LaDainian Tomlinson led the league with 1,474 rushing yards, and Clinton Portis led the league with 325 carries. These totals are the lowest for a league leader in each category since 1990.