Pohjakallio talks on DRM issues
It has recently been confirmed by Nokia's Pekka Pohjakallio that the reason for the original delay of the N91 was the inclusion of DRM. This delay pushed the N91's release from before Xmas to first quarter 2006. The register thinks that the N91 will be able to give the iPod a run for its money.
This has also been picked up by Darla Mack and Bizkero blogs. You can join conversation on delay on Mobile9 and GSMArena.