While you list the months of inventory in La Jolla as only 9 months, I always look at it from a different data point. I look at the number of single family residences listed for sale.
In 2006 and 2007 that number was almost always under 200 and in the slow season (winter) it was under 150. Currently it’s hovering around 280. The alltime high I’ve seen is just over 300 and that was at the end of last summer. Typically the number grows throughout the summer then drop after thanksgiving. Given that it’s at 280 and summer hasn’t even officially started, (well lest by memorial day to labor day standards) I suspect we’ll see record numbers of inventory before long.
One disclaimer I’ll say about inventory in high end places. There is always a good bit of inventory that is very unrealistically priced, and the seller is in no hurry to sell. How much of what is listed falls into this category? Can’t tell you, don’t know. But this class of seller makes the inventory numbers somewhat meaningless.