I just can not think of many sites I have developed over the years that do not need the ability to the owner or users to upload files. This is a very important topic for any web developer to understand. While not complicated, there can be a few things you need to remember and Bill Evjan has posted an article on MSDN about doing this.
One thing that has come up lately is file size limits. The Machine.Config sets the maximum file size to 4 MB. You can override this in the web.config for your site. I will do a little research and post the answer to that in another entry.