I wear my pony shirts all the time, especially my EqG and Sunset Shimmer shirts. I have a lot of t shirts for different things so people that know me just know I wear all kinds of cartoon shirts and stuff.
As for strangers, the only reactions I've gotten are positive ones, not only from fellow bronies but also from people who just thought the particular shirt was cool. I also wear 2 wristbands all the time, even when I am at work.