This subject comes up regularly in Singles forum, actually. In one fashion or another, at least.
But to answer the question, as long as our feelings were about equal for each other and she wasn't declaring her undying love for me when i'm thinking 'i'd like to get to know her more' haha. But as long as its on par to what i'm feeling then great. I enjoy the idea of a woman that can express herself on her own time and terms and not always have to wait for the man, then just respond back. If you really care for someone then you should express it, not sit around worrying about some silly cultural rule that says which gender should speak up first.