It is true that to read the articles the site asks for an e-mail address and that Mercola then sends you his newsletter. This newsletter is somewhat commercial, but also contains interesting health news. You only have to enter your e-mail address once and then the site recognises you by means of a cookie.
I do believe the Mercola site is safe though, as this is the number 1 consulted site about alternative health worldwide. Here's some information on Mercola's background: