I open carry for a variety of reasons:
1) It's Arizona. I can do so without any sort of permit or license. Why not exercise this right?
2) I live in Tucson. There's been a moderate amount of crime in the Tucson area in the last year or two, and it doesn't hurt to be prepared.
3) I would hope that a combination of myself being alert and aware of my surroundings combined with the open carriage of a pistol would deter any halfway-sane criminal from carrying out their plans.
4) It's much easier to simply open carry rather than carry concealed and worry about if you're printing or not. When I do carry concealed, I am concerned about printing or inadvertently displaying my firearm. When carrying openly, such worries go away.
So far, I've had absolutely zero reactions from people that were anything but positive or neutral. Nobody notices, and even if they DO notice, nobody reacts in any way (no double-takes, no turning suddenly away down a side aisle in the store, no store managers called to a checkout stand I'm at, etc.)
The two reactions I got were as follows:
* While buying ammo from Wal-Mart, a customer approached and asked if I could carry openly on the nearby indian reservation. I replied that I was unsure, and generally had no business on the reservation, so it wasn't something I troubled myself with at all. He thanked me for my time and went on his way.
* I was pulled over by the Arizona DPS (highway patrol) while on I-10 about 20 miles east of the CA/AZ border for some trivial violation (I think my taillight was burned out or something). When the officer asked for my license and registration, I informed him that I was openly carrying a pistol on my left hip. He inquired as to what type of pistol it was. I replied that it was a Glock 19, to which he smiled, said he had one at home, but the department issued them Sigs. We small-talked for a minute, and he gave me a warning and told me to get the light fixed.
Both were very pleasant experiences, and went off without a hitch. Assuming that it's legal for you to carry openly in your locality, I see no reason why you should not.
My only suggestion, if I may be so bold, is to not look like a slob (as I frequently find myself looking like -- hooray for being a student). When I carry, I generally try to present a positive image of gun owners by actually having my hair in some sense of order, shave, and maybe tuck in my shirt. Not suggesting you look like a slob at all (I have no idea!), but if one can present a positive image of gun owners while carrying, that's a good thin.