The first of the boomers aren't eligible for Medicare and SS (65 1/2) until just about now (end of FY11)
Medicare and SS only grew by $154B from fy08-10
Medicaid and welfare/unemployment grew by $328B (and that's not old people!)
2010-2011 was an even more distorted increase, but still, considering the total federal budget only grew by ~$650B between 08 and 10, and HALF of that increase was for Medicaid, welfare, and unemployment, we haven't seen the effect of the boomers yet, only the effect of liberal redistribution
Discretionary spending over the same period increased by $250B (and defense plus VA plus GWoT funding stayed about the same so you can't blame defense) HUD DofEd, EPA, State, etc made up the bulk of the increase, again favorite liberal piggy banks.
My point is, the 2006 and 2008 democrat takeover in the house (starting in FY2007) and Obama have created the bulk of the massive rise...even during the first 5 W years, spending rose from $2.0-2.73 trillion (roughly 6% per year), while 2007-2010 it rose by ~8%, and 2011 looks to be a nearly 10% increase.
This is pure unadulterated redistributive spending, not the effect of boomers. Spending vs GDP has only really spiked in the past few years.