It's no secret for me.
Friends know, and after a few dates, anyone I'm seeing knows. It doesn't define who I am, but I definitely don't keep it a secret.
The beauty of friends is that they're people you choose who like you for who you are. If they don't, they're not very good friends, right? My friends are mostly women, and they tend to have good taste even though most aren't really into perfume. Over time, they notice I often smell different, and every now and then, it becomes a topic for discussion. I've had a few friends privately tell me they bought fragrances for their boyfriends after smelling them on me. I think it's funny and flattering.
As for dates, I don't wear enough fragrance to be Cologne Guy, but after a few dates, anyone I'm seeing is going to notice I don't always smell the same. I mean, let's be honest, if I wore a different jacket every time a woman sees me, she's going to notice, right? And she'll eventually ask "How many jackets do you own?!" Scents are the same way. Eventually, I get asked how many 'colognes' I own since I often smell differently (because I wear different things on different days). It becomes a topic of conversation and I enjoy it.
I don't involve everyone in every facet of my life, partly because they're probably not even interested in some parts of it, but I don't keep any of it a secret.