Apple has apparently informed music labels that it intends to triple the length of iTunes music previews, extending the samples from 30 seconds to 90 seconds. The decision, according to an Apple message posted by SymBlog, was based on the belief "that giving potential customers more time to listen to your music will lead to more purchases."
Previews - or "Clips" as Apple refers to them - were originally 30 seconds in length, but will now be extended to 90 seconds. The shift will only affect songs in excess of 2 minutes 30 seconds in length; anything shorter will remain at the 30 second length.
It remains to be seen how the labels themselves respond. 90 seconds is roughly half the length of some tracks, and it appears Apple's only options are accept the longer Clip or pull your content from iTunes altogether.