Ive just come back from my 2nd trip to Prague, and this time i never left the room without it. Actually, i did just once, and we got a little lost. The maps at the back are acurate, and indispensible. The guides to places to eat, stay and see make it really easy to get around. We also found that if we stuck to places to eat that the book suggested, we would get good food/service. but when we went to resturants by chance we got ripped off big style.
Ive also got the Rough Guide to Prague, and this one beats it hands down. The information for out of town trips was also very good, and correct on train times/fares etc