It’s not allowed to use any electronic devices (including laptops) during take-off and landing. But apart from that you can use devices that do not submit/receive any electronic signals during the flight. So you can use a laptop (make sure you de-activate WiFi on it though), you can use an iPod, you can use a PSP, etc.
But you are not allowed to use mobiles, radios, walkie talkies and stuff like that at any time during the flight.
On some short flights (such as the ones from Dubai to Pakistan) they might stop you from using any electronic devices whatsoever. It shouldn’t be a problem on longer flights though.