I agree that email works best, as one can refer back to the content of the emails of either party at a later stage should any disputes arise. I do, however, like to meet the client at least once, at the business for which the website is for, to get a better feel of the clients' business goals and even the colour scheme, and sometimes the clients needs me to take photos too, which I charge extra for.
It is best if the client supplies all the content, which is what I request from my clients, but I usually do a little extra with that content, or if it is already enough, I do warn the client I may change it slightly to include some keywords necessary for better findability, so that they don't feel offended I've fiddled with their writing at a later stage - but if they're adamant they want their content to stay the same - I at least insist that I can do what I like with their meta descriptions and titles for the meta tag coding for each web page as want my clients' websites to be found - or it reflects badly on me!
The more content they give me the better, and if it's not that much, I advise that they should try give a little more. If they need, say a 500 word article on a particular subject written, I charge to write the article for them - and either my boyfriend or I write the article, after doing any necessary research on the subject.
I am aware I do a little more for my clients than many other web designers would, all inclusive, but while building my portfolio up, feel it is necessary. Looking forward to March next year when I've said I will be putting my prices up.
There are many things to consider when deciding how much to help a client with the content of their website, but, most times, the more they provide, whether or not you're charging them for any writing you do, the better.