There are still mainstream bands pushing concept albums and the long-song format. Look at Tool. Plenty of 10+ minute songs and their albums are very conceptual. But yeah, it's never been the most common thing; but it isn't going anywhere either.

 

Listen to this and then tell me what's the worth of 3:30 songs. There are lots of 5:00 plus songs there.

http://www.youtube.com/watch?v=Da1ZdmXidIg

But let me reiterate , it depends on a lot of factors. If you're going for commercial success it's better to have a song that's 3:30 long and if you're going for a cult success you just don;t care about the length of the song. You just do it as you think it's good. I never care, and I don't give a rat's crap about anything. I just do it be it 2:30 or 10:30. It depends on how I think the song should be like. Just like the Underworld. It's all in the feeling. No constrictions.

"King of snakes" The snake is untameable.

This is the best 1:30 you can pull at any dance party. Underworld are gods of dance parties. I know from the experience. Just let this play... especially after midnight.

My point is: you don't have to make a song last 3:30 to be successful. You just make it and see. It is easy to edit it to be shorter if needs be...

Cheers !