The Doctor wasn't as surprised as he could have been. After all, he and Rose had been living together for the past several months. Still, he hadn't expected a kiss right then. He was new enough to life with Rose that his reaction was much the same as it often was whenever a woman elected to kiss him without warning. He sat there and took it, only reciprocating when his brain finally caught up with the rest of the world, which unfortunately was rather close to the end of the kiss.
He blinked at Rose when she pulled away, clearly smitten with her and at a loss for words.