How does the Boeing 787 Dreamliner's glide ratio compare to other airliners?
As discussed here, glide ratio is related to the L/D (lift-to-drag) ratio of the plane. When talking about commercial aircraft, "glide ratio" is typically used to mean the ratio with engines inoperative. If the jet engines aren't running, they add a lot of drag, which will decrease the L/D ratio from the typical max value.

This analysis estimates the max L/D of the 787 at 20.8, while this site estimates 21.

Other sources estimate L/D of the A330 and A340 at 20. The 747 is estimated at about 18. So based on these estimates, the 787 is slightly better than other large airliners.

Most of the efficiency gains of the 787 are from the lower weight of composite materials (which allow bigger wings) and more efficient engines.