Maybe it's because I somewhat shy, but I just find it uncomfortable to look someone in the eyes for long.
No, that is just natural, if someone stares for too long into your eyes, it feels uncomfortable, so it does not feel comfortable to do that.
You just have to go with the flow of the conversation, and lose your self concious side, then, according to whatever the conversation is, serious, small talk, humourous, vaugley interesting, amazingly interesting...you find yourself giving the requisite amount of eye contact.
Like, if it's a convo where you are both having a right good laugh, there will be a lot of eye contact, but if you become self concious of that, esp if you are talking to someone you like but don't know *that* well, a budding friend or someone you fancy, you might overdo it and end up giving too much eyeball and risk putting a dampner on the laffs, but if it is a v funny convo and you are getting on, you will be let off with some overeyeballing, and the convo will resume as normal. and that is just one example, there are others, like if it is a deadly serious convo, say something sad has happened in the person's life, you will probably find yourself keeping eye contact for a lot of the time you are talking, but have them on immediate eyeball drop standby in case you overdo it, perhaps dropping the eye contact as soon as you have made your point, so's it does not feel like you are prying into the person's pain. Giving them some emotional privacy, but not so much that you are not taking time to check they are alright.
I am just thinking about this as i type it up, in words, is sounds so complicated, but in action it is very natural, and you do these things without thinking about it too much.
But, if you are self concious about yourself at all, chronic shyness or whatever, then you will find these natural responses come out fractured somewhat. So, you have to try and lose that, I mean, you sound like you have a handle on what is appropriate if you don't feel natural staring into a person's eyeballs for too long, you shouldn't.
Up until a couple of years ago, I used to avoid all eye contact with strangers while i was walking down the street, because I was very self concious physically, just wanted to frickin' get past them as quick as possible, lol.
But nowadays, I look at a lot of people in the street, and you do get all kinds of reactions, as you say, it's very interesting. I always feel sorry for the type that I used to be when I look at them. I want to chase them down the street and shout 'It's ok! don't freak out! I used to be a self concious nut as well! Just look! Look in people 's diretcions and eyes! It's ok! It's interesting and sometimes you even get a cool look of recognition as if you are both on the same wavelength or something, like us!' lol
but i don't of course, but if i do end up in a convo with someone who is like that, i try to put them straight on the whole eyeball dilemma, and how it is not such a big deal, and how i used to be like that. I suppose much as i am trying to do now.
But, i can see why it can be such a big deal for some people, for instance, i don't blame a woman if she looks quickly away from you, as a lot of guys will be giving the leery eyeball, and that is what they are used to, but sometimes you will past a cool, smart girl with good instincts and they will give you a cool eyeballing back as they know that's not why you are eyeballing them, you are just being friendly and curious about people.
Also, if it is late at night, and I am the only person on the street and another person comes towards me i almost always say 'hello.' 'hi' or 'alright?', and give a small amount of eye contact, just to put the person at ease somewhat, and it's v cool when the person says 'alright.' back at you, they are almost relived you are not some night time nut, lol, common courtesy moments between strangers like that is great.
edit: also, posting up massive posts can be like giving too much eye contact, so sorry if i freaked you out there, but if you want an answe beyond, just be natural with it and don't be a weirdo', you have to go into *some* detail. now, please stop reading my post/looking into my eyeballs, you are freaking me out.