I wouldn't care too much about the whole summer/winter thing. As you mention yourself, it's all about smelling nice. There are, however, some very heavy fragrances that are just too much during the summer. Imagine somebody wearing a good dose of A*Men on a 40C summerday. That would probably kill people who passed by. However, this is just a general opinion - if you can wear a couple of sprays and it smells really good, then of course that's no problem at all.
Some fragrances are classified as summer, because they have a cooling, o-zone-like effect. If you wore Kenzo L'eau Par in a cold winter day then that would just add extra cool coldness to the cold day. It can also be hard to smell aquatics in the winter, simply because the cold (at least here in DK) can be so tough to your nose, that you can't even smell certain fragrances. I think that's why most people use heavier, more powerful fragrances in the winter.
If you find out that you smell good with Envy on a hot summer day, then who cares if it's a winter fragrance? If you feel like wearing a summer fragrance in the winter and it smells good, then I guess most people would just appreciate it. There aren't really any rules except to smell good. Winter/summer are just a general guidance.