I've only been out there for short vacations, but you can hammer. The climate is great in Nov-May and its not very windy for much of the winter. As noted above, Tram Rd. is one of the steepest 3-4 mile climbs in So Cal and it was just repaved. Its considered the fastest descent if you are foolish enough to ride that fast. For me, the downside is monotony of flat, straight road in the coachella valley. There is a lot of it and plenty of bike lane.
Ride with this group. You'd be surprised at the horses out there. Especially the retiree ones.
http://www.cycleclub.com/