It has the best winery and offers a tour which is well worth it.  It even includes tips on tasting wines.  For the golfers...Ely Callaway began the winery as a retirement hobby and sold it to go on to start Callaway golf.

Temecula is far enough off the coast that it is in the desert area of Southern California; however, a "mountain" pass still allows cooler air from the coast to bring moderate temps and a bit of moisture into the area.  The conditions created are perfect for grape growing.