He couldn't exactly say that he was comfortable around Uhura; Spock was much too uptight for that. But he found it was easy to talk and so he continued to do so, finding a lovely sort of rapport build between them. He liked listening to her talk about herself.
It was only when they stopped that they realized the little coffee shop had emptied sometime between their arrival and the close of their conversation. Time had sped by as they'd gotten to learn a little about each other. With the wait staff giving them just barely veiled ugly looks, the pair tossed their long-empty coffee cups and headed toward the exit.
Spock, nervous and slightly self-conscious, was the one to suggest they maybe do this again sometime. Phone numbers were exchanged and Spock went home feeling lighthearted. There was just something about spending an evening in discussion with a pretty girl.