Lets face it most of the crappy pop put out today can only be endured for 3 min before you have to switch it off. LOL

Contrary to what Marc says, outside of Nashville people are still writing, performing and recording good successful songs that last well in excess of 3 min. The average modern indie rock song by chart topping artists usually last at least 4min or even more.

I would worry more about the quality of the song than its length. A good songwriter should know instinctively what length a particular song he writes should be depending on genre, market he is aiming at and tempo etc.

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055