Many folks visiting the SLO area assume we're pretty slow (yes, back in the 70's we were SLO-TOWN. not anymore) and that dinner reservations are not needed.
This is no longer the case, except maybe in Jan-Feb. When planning a trip here, it is safest to call ahead and reserve. The place I work had 3 large parties calling for reservations yesterday for tonight, and were all told they'd be on a waiting list. They may end being dissapointed, or eating at 10.
This weekend, there are large events that have pulled thousands of chow hounds into the area, so if you haven't already, get on the phone and reserve. A few restaurants don't take reservations at all, and force you to hang out in their bar--so take your chances there.
Just sayin, its not a good weekend to leave dinner till the last minute!