So, no, it doesn't mean the federal government can do whatever it wants.
http://www.dailypaul.com/103339/thomas-jefferson-clarifies-to-provide-for-thegeneral-welfare
Um, Jefferson was 1 author among many and his opinion is 1 opinion among many.
Very true! Here's another opinion, from James Madison, the "Father of the Constitution"
"With respect to the two words ‘general welfare,' I have always regarded them as qualified by the detail of powers connected with them. To take them in a literal and unlimited sense would be a metamorphosis of the Constitution into a character which there is a host of proofs was not contemplated by its creators."