You can e-file a 2011 return provided that the return in question qualifies as MeF. This holds true for most federal return, and a few states... notably, OH, NY, and CA. Most states, in 2011, were still legacy; therefore, most states will have to be paper filed for 2011.
For 2010, roughly 25-30% of federal returns were MeF, and no states were MeF. If your ATX 2010 program will allow you to create the e-file for the federal return, then you can safely transmit it; however, you will have to paper file most federal and all states for 2010 due to this.
This holds true for individual returns; the IRS will accept e-filed business returns for current year plus two years back and most states will as well. Some states require they be paper filed for prior years.
The IRS, in 2011, stated and posted that this is how it is going for individual returns going hereon out. For next year, you will be able to e-file 2013, 2012, and 2011 returns provided they meet the MeF guidelines. 2014 will see the e-filing of 2014, 2013, and 2012... at which point every individual return, with minor exceptions, would be MeF.