On Sony’s official site ( Japanese) they have just posted the following in bold, red font::
" CAUTION: This update is only for customers who obtained PSP® ( PlayStation®Portable) for Japan which model number is PSP-1000 or PSP-1000 K. Upon completion of preparing, we will announce update information for the other countries/areas customers via SCE Group Web Site or other channels . For theses customers who obtained PSP® in the other countries/areas, please DO NOT update PSP® through this web site."
So, the choice is up to you on weather or not you upgrade. I’ve got two PSP’s and I plan to upgrade one, but I’m going to wait for the US 2.0 Firmware release. Ya’ never know eh?
Source : Sony Japan
http://www.playstation.jp/psp/update/ud_01.html