In the NY Times Bruce Bartlett has a table showing the composition of the approximately 47% of households that doe not pay income taxes.
Yes, you are reading that correctly. Conservatives who are opposed to raising taxes make an exception for those who do not pay taxes, meaning they want to impose taxes on 40.7 million taxpayers making less than $16,800 per year.
Why? Well where exactly did you expect them to get funding for more tax cuts for the wealthy? Ok, that's not fair. They cannot get enough tax revenue from tax increases for the lowest income groups, they are going to have to cut government spending that benefits those groups also.
And finally, for those of you who think the people who do not pay federal income taxes are getting away with paying no taxes, there is this article here.