Resident vs. Non-resident alien choice

I understand the difference between the two (I think).
What I don't understand is why anyone would choose to be declared a resident if you get taxed on worldwide income. Can someone please help me out!?!
I started working on a TN visa November 1, 2010 but can make the choice to be declared a resident alien. With so much written about it and topics on here about how to get this status, I feel I must be missing something.
Thanks!!
(Steven, I hope you're still on this site since your answers are always helpful)
PS, I'm married to an American citizen if that changes anything...

Well, the main reason one would want to be considered resident alien would be due to the better tax rate that filing a 1040 has over 1040NR.

Add to this thte fact that you are married to a US citzien, who laready has to file a 1040, this allows one to file jointly, by reporting all year income.

Most Cdn residents don't pay any extra tax to US on their Cdn income, because of various credits and exclusions, which would likley be your case, too.

Another reason a Cdn might choose this status, is if their Cdn tax non-residency is murky. By filing a 1040, one can show CRA that you were indeed intending to be a US tax resident.

As a Cdn citizen, you don't even have to formally make this choice, simply file in which ever way benefits you for 2010: 1040NR for whole year, dual-status 1040NR/1040, of full-fledged 1040 jointly with spouse.

any more clarifications can be found at forums.serbinski.com