"a not unintelligent man"?

Dear all,
What do you think of the construction "a not unintelligent man"? I know it is not prescriptively approved, but is it normal in actual speech? I would appreciate as many as native speakers' replies as possible and please reveal the variety of English you speak before providing your valuable opinions.
Also, what about the construction "a not intelligent man"? Is this form as commonly accepted by native speakers as "a not unintelligent man"?
Thank you very much.
Ray