There have been changes to the laws that effect HOV carpool stickers in California. Here’s a summary:

Yellow HOV decals will be extended 6 months until July, 2011, after which they will expire permanently. White HOV decals continue to be available for pure zero emission vehicles. A new category of decal will be offered for the next generation of alternative fuel vehicles, including plug-in hybrids. Up to 40,000 of these will be issued and they can be used until 2015.

You can read more about changes coming to CA HOV decals