Well on my main site I do ask the customer to register because I need to send them a download link via email, however all I ask for is there email address and no other infomation.
I am also developing a ecommece solution to sell, and with this I have elected not to require registration, but at the checkout I would require the customer to provide Name and address to enable the goods to be deliverd to the customer, they will have the option for me to retain there data so that they will not have to fill it all in the next time they return.
On a personal note I hate having to register and will avoid it if I can.
I even fell out with Curries, when we bought a carpet cleaner they wanted my name and address for the gurrantee they said.
I said I will not give u that information, they even feteched manager out, I asked him if he wanted to make a sale or not, and told him he would not be making a sale if he insisted on having my name etc, he decided he could manage without it, so he made the sale.