I discovered Cafe Royale over 4 years ago, and it remains one of my very favorite bars in SF. The reasons: friendly people (both behind and in front of the bar); a warm, open space with comfortable seating and great evening light; jazz on the speakers and Boddington's on the tap; a fine blend of upretentious people of all ages, backgrounds, and locales.
Cafe Royale has always been a great place to lounge with friends after work and converse at comfortable volumes. In the last year or so they have also added some quality events later in the evenings, such as art exhibitions and live music.
My only complaint would be that evening events can get crowded. But Cafe Royale is a unique space in San Francisco well worth checking out.