I'm a pretty new user of the iPhone and the lack of arrow keys has bothered me from the beginning. It did help when I learned how to get the little magnifying glass to scroll around most windows, but to me that is still not the best way to quickly navigate through long strings of text such as an e-mail.
The case that drove me the most crazy was when I was trying to post on a google group message board. The box to type in is a fixed size within the window, and when I had gotten to the bottom it kept scrolling down to add more text (as I expected) but there was no vertical scrol bar or anything to go back up to the beginning of what I had typed. I was eventually able to get it to go up using the magnifying glass, but it was a very cumbersome process and a lot of times it seemed like I was just swiping my finger to go up on the entire page, rather than just within the text box that I was typing in.
I believe arrow keys would have been MUCH more efficient to quickly scroll up and down within the post. They wouldn't even have to be on the "main" keyboard screen with the letters.. I wouldn't care if I had to flip to a different screen such as for the letters/symbols in order to access the arrow keys, but I definitely think that Apple should include them in the next version of iOS! Consequently, after struggling to type a fairly long post on an already small keyboard, about the time I was about to submit it Safari somehow crashed on me and when I went back in everything I typed was gone anyway... so I just gave up until I got home to repost from my WINDOWS 7 PC! I think I'm going to have to check if Android has arrow keys on the keyboard... if so then that could be a deal-breaker for me next time I upgrade my phone, if Apple hasn't come to their senses by then!