I must disagree with those who think its a bad idea. Shopping with a girl is a great idea if its for you, and you have $. They can style you like no other, and they know exactly what looks sexy on you. Plus, you can pull them into the changing room with you while you change and tease them as you undress/redress.
I think many who have said it's a bad idea have never gone shopping with a woman. There is no way to say that it would be a good/bad idea, it's all going to depend on how you treat the experience.
You can get her opinion on colognes, styles, outfits, etc. I've gone with 3 different ladies and had a fantastic time.
I will say that don't go unless your ready to spend some $. Even a few decent outfits can cost you $300-500.
Have Fun!