wowowo be careful with that "If you are in the US for less than 5 years, you don't have to pay those tax on your H1B income" as this statement is completely FALSE.
its true that for OPT u dont have SS and med tax, but for H1B, which is treated the same as a U.S. citizen for tax purpose, is by law subject to ss and med tax. see IRS "Aliens Employed in the U.S. – Social Security Taxes"
only under two circumstances where you won't have to pay ss and med if u r holding H visas..that is if u hold an H2 or H2A
