IntlTax:
I disagree, though I AM making an assumption in my explanation below, that assumption being that PK123 filed Form 1040, 1040A or 1040EZ as an H-1B visa holder in a tax year previous to 2007. If so, then the IRS DOES consider him/her to be a U.S. resident for tax purposes by virtue of the fact that he/she filed that prior-year resident tax return.
Further, even if PK123 never filed the resident tax return, the IRS will ASSUME, by virtue of the fact that PK123 has a H-1B visa, that he is a resident alien if the H-1B visa was effective prior to 1 January 2007.
In other words, PK123 will have to make the case that he/she has NOT met the Substantial Presence Test in order to avoid taxation on his/her 2007 salary.
If he/she met the test prior to 2007 by filing a resident alien return, he/she remains liable for all world-wide income in all subsequent years irrespective of his/her physical location for the duration of his/her H-1B visa unless and until he/she formally revokes/abandons the H-1B visa.
Just my humble opinion...