If a business is incorporated outside the US, but has a good percentage of users in the States plus a 5% of workforce there (independent contractors), what are the tax implications?
There are only tax implications for the business in it's domicile of jurisdiction (where the business is organized).
Contractors in US will have US tax implications, if they actually reside in US. If they live outside US, for more than 330 days/year, they qualify for the Foreign Earned Income Exclusion, which is detailed here:
http://www.irs.gov/Individuals/International-Taxpayers/Foreign-Earned-Income-Exclusion
