I have just returned to DC after several days in SF and thought I'd post some additional experiences (I already noted my very nice dinner at La Suite earlier).
Slanted Door: I took myself to lunch here after having seen several articles with the chef's recipes in the NY Times. I had also noted that there is a wide range of opinions about this place among SF posters, and so limited myself to lunch there 'just in case'. As it turns out my fears were unwarranted. Not only did they make this solo diner very welcome and comfortable, but they even gave me a table rather than having me sit at the counter like most other solo diners (and just to set the record straight, I did offer to wait rather than occupy a table needlessly, but was told it was not a problem despite the fact that the place was packed). My waitress was extraordinarily helpful, making a number of suggestions including pointing out that I could get half-orders of any of the appetizers (since I had a hard time choosing among them). In the end I had the Slanted Door spring rolls and the daikon rice cakes to start, followed by the clay pot chicken. The spring rolls would not normally have been my first choice, but I was told that they are a 'big deal' so I relented, and they are the one dish I regretted ordering. Sure, they were tasty and all, but they were no more tasty than similar rolls I have had at countless pho places in DC. The daikon rice cakes were revelatory, however, and the chicken was excellent (as good as the version I made, if I do say so myself, so perhaps I should have ordered something else in hindsight).
Cortez: I had been told that this was a great place and had made plans to dine there with friends one day, but an additional person joined our party and they could not accommodate us (!) so we went elsewhere that night (see below). I made a reservation to go myself a few nights later and arrived to find that they were closed because of a water main issue. No phone call, no nothing, so I went elsewhere again (see elsewhere below).
Isa: This is where we went the first time I did not go to Cortez, a similar idea of a restaurant serving "small dishes" that are somewhat similar to tapas. The room is not too big, though they expand their space into the rear garden (under a canopy) where tables are pretty tightly packed. The waiter advised us to go for 6-9 dishes for our group of three, which worked out pretty well. Our dishes included a risotto with truffles and mushrooms, sautéed pea shoots, potato soup, foie gras with mushrooms, arugula salad with figs, beef tenderloin and a sea scallop dish. Of these, the only real standouts were the foie gras, which was done perfectly and had a combination of flavors that truly complimented the richness of the foie; the scallops, which had a very oceanic flavor in addition to natural sweetness enhanced by slight caramelization; and the risotto, which was cooked perfectly and whose truffles gave it that wonderful earthy flavor. Desserts were not so great: I had a hazelnut semifreddo that was actually just ice cream (I guess they did not realize that semifreddo means semi-frozen).
Swan Oyster Depot: OK, I know this is a bit of a tourist place, but I really love oysters and could not pass it up. To my surprise, considering the places size and its popularity among tourists, the service was extraordinarily friendly! I got a seat at the bar quickly (it was for a late lunch) and wound up seated next to some regulars. My clam chowder was as good as anything I have had back East, and the kumamotos were extremely sweet. A bit pricey, perhaps, for what I got, but I left content.