Whilst we didn't need reservations, I'm sure in peak tourist season they're necessary, if only because the restaurant was so good. We had very little time free for lunch after the calamity at the Sonoma Cheese Factory and were treated to a truly great hamburger with superb service, terrific ambience, and (unsurprisingly) even more terrific wine. If you're staying in Sonoma or just passing through, they're more than worthwhile for a quick bite or a more leisurely stay.