First off, I can't stand the term "code smell" anymore.  It is used too often and is much of the time thrown about by people who couldn't recognize good code if it bit them.  Anyways...

I personally don't like using a lot of regions.  It makes it harder to get at the code, and the code is what I am interested in.  I like regions when I have a large chunk of code that doesn't need to be touched very often.  Aside from that they just seem to get in my way, and regions like "Private Methods", "Public Methods", etc. just drive me crazy.  They're akin to comments of the variety `i++ //increment i`.

I would also add that the use of regions can't really be an "anti-pattern" as that term is commonly used to describe program logic/design patterns, not the layout of a test editor.  This is subjective; use what works for you.  You are never going to end up with an unmaintainable program due to your overuse of regions, which is what anti-patterns are all about. :)