Pros; With vector it is very simple to resize the icon both up and down, smaller and larger, without worrying about losing any detail to the image.
Cons; With vector you lose any hope of the amazing details that you get with bitmap. Vector can be looked at as a simplified bitmap. You can take the basic shapes from the bitmap and vector those, but you can never have the same amount of detail tat bitmap gives you. It makes it much cleaner looking, but that's not always what you want, which is the case for me. I do not want to lose the bitmap. I want all of those subtle(and not-so-subtle) details in my icons.
Pros; With bitmap you keep all of the quality of the image(the photo). Bitmap has all of the subtle detail and gradients that no matter how hard you try, they can never be reproduced vectorally(may not be a word but it works well here). Bitmap gives me all of the subtle vein-like details within my marks.
Cons; With bitmap, resizing is much more difficult. It is very simple, and very successful, to size down a bitmap image, but sizing up is a whole different thing. When sizing an image up, you are requiring the computer to create more information that what it is given, and it is prettyyyyyyy bad at doing that. When you size up an image, it becomes blurry or pixelated, which is almost never wanted, and almost always very ugly.