As tweeted by developer Jackoplane, Siri is now ported to a jailbroken iPad 1. As you already know, Siri was ported to iPhone 4 a week ago and now we have it on the iPad.
However, the same iPhone 4 problem resides; they still haven`t connected it to Apple`s servers which means Siri is a still a silent agent, and until that problem is fixed, the iPad`s unofficial assistant will remain ineffective.
Hopefully, that will be fixed soon.