This is a must drive road in North San Diego County. It is hugely popular with motorcycles, cyclists, and all manner of car clubs. It is so popular that there are several photographers out there almost every weekend. The most popular is up/down the south grade. A loop is possible using East Grade. There is a restaurant at the top of the mountain making a good rally point. Palomar goes through phases of high enforcement, usually after somebody tries to fly off of the mountain. It does have mixed traffic so be careful of cyclists.
Speaking of cyclists......check this out! Shocking Motorcycle Crash into Bicycles 4/27/2013 - YouTube