The filing date always stays the same (ed: Sorry, I meant priority date there) - but, yes, that's my understanding:
http://en.wikipedia.org/wiki/Patent_Cooperation_Treaty
USPTO has a diagram here: http://www.uspto.gov/web/offices/pac/mpep/documents/1800_184...
Under their system, it the whole process (to what they call the national phase) can be 30months - it varies from country to country, but 30 seems to be common. http://www.wipo.int/pct/en/texts/pdf/time_limits.pdf
Re:Ask HN: To Patent, or Not To Patent
by gravitycop on Friday January 16, 2009 @03:01AM
(#436327)
OK, thanks. I should have checked on this information before posting. Sorry.
[EDIT] I stand corrected. Apparently, there is an international (PCT) route to U.S. patents. http://www.wipo.int/pct/en/pct_strategies/the_third_way.pdf [PDF]
the “international route” of the PCT to U.S. patent issuance. [...] THIRD WAY IS BEST WAY This Third Way of using the PCT as a matter of domestic U.S. patenting strategy gains many advantages for the applicant to control the timing of search and examination of the U.S. application, if one begins with a Provisional Patent Application.