A good time to invest in San Diego real estate is when you fall in love with a property. San Diego will always be a desireable location to live and work, given it's favorable location and climate, and so, given today's low interest rates on loans, and the wide variety of properties and condos and mansions available, it MAY make sense to start looking now -- if that fits in with your life plans.
It's still somewhat a buyers market now. If the time is right for you and yours, I'd begin looking. I know of 3 different listings at more than $2M that sold within 2 weeks. I personally just had a home listed ($360K) and it has just sold in about 1 week. Lots of variety out there right now. Find a good agent who will represent you well.