I agree with those on this board who have said that most things will come out in due course -- whether or not you want children/how many, parenting styles, spending habits/approaches to personal finance, lifestyle attributes, etc. There's really no need to sit your prospective honey down interview-style and say things like, "I would like 2.5 children. Would you also like to have 2.5 children?"
However, while I am of the camp that "the talk" is mostly unnecessary, there is one thing I believe is important to establish pretty up front: whether or not the two of you are on the same page as far as level of commitment desired. Is this dating for fun, or dating with the intent of finding a life-partner? If you're the type that sees dating as a means to an eventual end (i.e.: marriage), then there's no point "wasting your time" with someone who either a) isn't open to marrying anyone, ever, or b) is not at a point in his/her life where s/he wants to commit to a long-term relationship just yet. Don't get me wrong, I do not judge those who enjoy "dating for fun;" it just doesn't suit some people (myself included). Personally, I wouldn't consider dating anyone who doesn't see dating the way I do: as a way to figure out what you want in a life-partner, and as a means to eventually FINDING that person who you want to spend your life with.