Just on the principle of fairness, I'd say that both parties should shell out for dates.
However, the individual situation may not work as neatly, and may need to be tweaked based on personal circumstances.
For instance, I'm too cheap to be willing to eat at a restaurant or see a movie in a theater.
But I would also never, ever expect or demand that a guy pay for me. This can be cause for awkward situations when it comes to going out, since I don't want to pay, but I don't want to be paid for, either.
So with my first boyfriend, we solved this by simply not going out. Neither one of us had to pay, and we were both happy. He bragged about how low maintenance I was all the time, and I didn't have to break the bank to date a boyfriend. It worked for us.
My second (and current) bf was different. When we started dating, I was still a (starving and broke) student, but he had already graduated and had a job. And I was/am still too cheap to go out.
But because he *wants* to go/take me out, he does pay for everything. When this first started, I felt so uncomfortable, and I asked him time and time and time again if he minded. But he's completely willing to pay, and he actually uses me as an excuse to treat himself, because without me, he's also too cheap go out.
So this works, too.
However, I do pay him back in my own way. For instance, I bought him all of his groceries with my spare meal points during the semester, because that didn't cost me "real" money. We both agreed that it was a fair exchange. But if we were to ever start living together, we'd split rent, utilities, and groceries 50/50, no question. There's no way I would live off someone (with the possible exception of parents in an emergency situation).
So the bottom line is: if your gf has the money and is willing to spend it (on herself or on people besides you), then I'd take it as a hint of selfishness if she always expects you to pay for dates. If you're in a serious, long-term relationship, contributions really should come from both parties, unless specifically agreed upon in advance. However, being too nitpicky about the exact way expenses are split can also be a source of discord. So it's a fine balance.
~mimi