At the title says there is a hack out now to allow you to use Siri for dictation on other Apple devices.

Full story here Install Siri Dictation On iPhone 4, iPhone 3GS And iPod touch 4G Using Siri0us | Redmond Pie

I have done it on my jailbroken Iphone 4 Running Ios5.

Works great.

yea , dictation side works really well ,its not the full sri but its the next best thing