Working In and Around the US of A?

jackda asks: "Like many out there I (an Engineer from Canada now in Massachusetts) am working in the US on the TN-1 visa. It has and continues to be a frustrating process both obtaining the visa, as well as obtaining information on working as a visa holder, in the US. I have received a very mixed bag of info from the US/CDN Consolate down to the border cross/INS people. I am just wondering if the collective minds of Slashdot could offer any tips, sources or info on anything from SSNs, to taxes, to resident/employment status, to any useful knowledge about living for a TN visa holder."