I'd just like to give Tree People and the Coldwater Canyon park trails a big 2 thumbs' up. When I went up there this morning, Tree People volunteers were spreading mulch on the trails (v. muddy from last night's rain), so not only were the wide paths well-maintained, they smelled good, too. A popular but not over-crowded trail with great vistas of the Valley and Laurel Canyon (I'd upload photos of LA, but my sister took my camera to CT), it's a great hike, and you can do it a couple of different ways. Moreover, you'll get cooler, low-key celebs, like Jon Heder, who I think may have been one of the Tree People.
Then on my way home I saw Harold Ramis driving out of Ralph's in Studio City.