Yes, it pushes your rear tires out flush with the fender flare. Purely cosmetic and only needed in the rear if appearance matters. Here is a shot without the spacers:
http://www.onlineautoshow.net/img/S87-18frontq.JPG

LPMM,

Once again, thank you for insight and help.

would you guys recommend running 245/45/18 tires? What would be the advantage and disadvantage?

uh - on a X5? I wouldn't. Maybe on a X3. 245-45-18 is going to be a about 1" shorter than a stock size tire. Stock size for the X5 are 28" tall - 255-55-18, 255-50-19, 275-40-20 for example. 245-55-18 might be OK, but I would just stick with the stock 255-55-18 if running 18's.

I just received my style 87 18's yesterday. They look awesome I can't wait until I get some winter tires tomorrow from tirerack (pick up, they're now in CT). I'll psot some pictures once it's installed. Once again, thank you to everyone that has contributed to my request.

did you say someone locally was selling them? i'm looking for a set of wheels only.

yes he was, I got it delivered to my house last night. I got it for $300 and the rims are in awesome. I can't wait to get the tires tomorrow; perfect timing because we're having a snow storm tomorrow. I can't wait to test out the Blizzaks.