taller than average ceilings

Reduced ceiling reflection, and a lower "floor to ceiling" bass node (which should be a good thing)

It can however be less than fortuitus if it matches the room length or width.

I have had the opportunity (and luck) to listen to three different gears in different houses, comparing normal heigth ceilings with high ones, and I always liked them much more in the high ceiling houses. Treble and medium frequencies sound more natural to me in high ceilings houses.

Hopefully your ceilings are tall and flat. Mine are cathedrals and I'm convinced this is one of the worst configurations possible to manage for great audio. The RMAF website has videos of an interesting dialog on the subject with Jim Smith (Get Better Sound) and Charles Hanson (Ayre Acoustics).

http://audiofest.info/2011/video_player.php?video_id=21&Sid=fec2d4851b7bef5ad0631ad20a7e25bd

Best,

My room is 15' x 22' with 18' ceilings. I have found that the choice of speaker is important; some speakers that I have tried "die" in the space while others excel.

I believe the taller ceiling will help with the sound, adds more cu. ft to the room. Speaker placement is something you will need to tweak. Should be close to the same as if you had 8' ceilings. Should add more ambience to the sound stage.
Joe Nies