Personally I'd always prefer to not include any links that have an href="#", but I guess it depends on context.
Although using id/anchors as navigation within a page is perfectly valid, I can't quite see a reason to provide an empty one, although without an example this is all pretty subjective/conjecture.
I don't think I actually answered the question there....
I guess it may well be treated by google as a link back to the current page, but I'm not entirely sure how that would hinder, or help SEO at all.
Realistically, there's not a situation I can think of where it would be a good idea to provide a totally dead link though.
Answer. Doesn't matter, but still, don't do it anyway....!