I always prefer the <input>, since the <button> shows trouble sending information when it comes to IE in general. Although there’s a javascript that’ll fix it, I wouldn’t trust it to have the job done. And it’s easy to have a gradient background on an <input>, but if you want to style it like a <button> – you’ve got a challenge (especially cross browsers).
I do believe it was Eric Meyer who said something like: Because browsers usually take somewhat controll over <input> elements, I don’t give them much style.
