1) If by wide screen you mean requiring a horizontal scrollbar, the answer is no. I have yet to see a good UI that's wider than a single page. If you mean layouts that fill screen width, I've had some success there (Photo sharing/video sharing websites with grid content are good examples)

2) As little as possible. A typical reaction/animation time should not take more than 300 ms. The key is to test it on slow machines and connections, and optimize for that delay.