An American correspondent, working in sales, notes that 'salespersons think too much of themselves and use I far more than they use you (the person to whom they are selling', and asks if I have any comment as to why it is so overwhelming? (I take it that 'I' here includes 'me', 'mine', 'my', and 'myself', and 'you' likewise, 'your', 'yours', and 'yourself'.)
I think this is a question more for psychologists than linguists, actually. But it's a commonplace of discourse analysis that a conversation doesn't work so well if one of the participants keeps talking about himself/herself; and hardly works at all if both do. The point has often been discussed in relation to such issues as gender roles - I seem to remember it coming up in Deborah Tannen's writing, for instance.
Certainly, I outranks you in all the frequency charts. I've just looked in the British National Corpus and find that I is the 11th most frequent word, whereas you is the 14th. But this hides an important distinction: in speech I is 2nd and you is 3rd, whereas in writing I is 17th and you is 21st. The contrast is greater in US English, it would appear: in the Brown University corpus, I is 20th and you is 33rd. Does this reinforce the stereotype of the British being more self-effacing, I wonder?
It's difficult to compare corpora, as they are based on very different samples and genres. And genre is critical. In the Brown corpus, for example, Romantic Fiction was the top genre for the use of I, followed by Belles Lettres and Biographies. Romantic Fiction was top for you, too (I guess because everyone keeps saying I love you), but second was Skills and Hobbies (the 'you' of instruction, I suppose).
I reckon I would be especially common in blogging, and you much less so. I remember the other day consciously avoiding a use of you in an initial post. But - having just looked back at a couple of my blogs - I see I do use you quite a bit to mean 'one', and just occasionally address 'you-all out there' as you. When the blog gets a comment, then you probably becomes more frequent. There's a thesis waiting to be written here!
The crude stats don't tell us anything about the functions of the pronouns, though. In the sales situation, I imagine there are important differences between the I of exposition ('let me tell you my experience of this product') and the I of egotism ('let me tell you about me'). You also has several functions - apart from its conventional second-person use, it can mean 'one' ('you see it often...') or even replace an I (someone who says 'It makes you sick when you see something like that' usually means 'It makes me sick when I see something like that'). If a salesman has personal experience of how a product works ('I have one of these at home...'), then it would be relevant to tell me about it. And too much use of you might be intrusive. A pronoun balance, I suspect, is what's needed.