Ah ... too old to worry about style
I will often break out the vest if I am doing a lot of work in a small area. When doing architectural stuff, I hate lugging the Billingham bag around. The vest is a Hasselblad branded one that looks just like all other vests from Canon etc.
In it goes all my cards, lens cleaners, filters, and whatever lenses I will need for the next few hours (16-35, 24 T&S, 24-105 and 70-200). It makes is exceptionally easy to switch gear rapidly with no bending over and no dropping bags into puddles.
As has been mentioned, vests can be tough on backs for some reason and I might look ino belts sometime. But, at present, it is a great tool in certain situations and definitely plays an important part in many shoots.
If I am just wandering for non-commercial stuff then I tend to use the Kata bag.
Mike
http://photosignals.smugmug.com