I think people who know you, notice a difference in you before you do. I mean, you are seeing yourself every day so its hard to notice any sort of change.
-the other day my mom told me "your nose got narrower and your neck is so slender"... totally unaware of that myself
-my wife hugged me and said "omg, i can put my arms around you entirely, so weird"... didnt even realize it
-my friend who i dont see very often told me "whoa your face is like CRAZY soft now..." and to me it looks mildly soft at best lol
-other changes include my big brother telling me "you look so much happier now, I can't explain how but I can see a glow in your eyes that was never there in the entire time you've been in my life, until now"
my mom also told me last night "wow, your waist is starting to look very nice"... which i find the most fascinating because i don't really see a difference in how my waist is now compared to before...
But all in all, my personality, disposition, attitude, emotional output ~ it all has proven to play a huge role in the differences people see, sometimes a person will tell me "your eyes look brighter" but in reality they aren't brighter, i'm just happier. People are most astonished by my newly acquired fluffy personality ~ i'm giggly, smile a lot, always talking, a bit dainty, and it makes me appear smaller than I actually am (even though I still measure 6'1", my wife tells me "youre not as tall as you use to be... i feel like you got smaller") amazing how people's perception of us can radically change by such minimal factors. And the reason I say that people are most astonished by it (and constantly reminding me of how it blows their mind) is because before transition, i was a very angry, very ranty, upset person who was loud and aggressive and so deep in the closet that when my guy friends found out, they said "but how!?!?! He's the MANLIEST guy I know!!! He's manlier than me! (said a friend from the Marines)"
So yes, i think others notice the changes in you before you do, but often times its more strongly driven by your outward attitudes and not so much by the small physical changes. Its almost like comparing it to how big a difference waxing your eyebrows can have on your entire face.