Hmm. I suppose I have done enough road construction to give my opinion on lowered speed limits.
At least in Europe, the visible sign is the one to follow, and the area it affects starts immediately behind it. So when a lowered limit sign is visible, according to law you should drive at the lowered limit. Nothing complicated about that. Actually, one of the biggest arguments in the project I'm working on at the moment is about lowered speed limits under a pair of bridges. Our opinion is that the limits are lowered all the way until all work under the bridges is done - it's one of the most dangerous environments to work in, on a dual two-lane carriageway under a bridge. Our overseer, a good-for-nothing lineage planner, simply cannot understand it, but we have managed to shut his gob nevertheless.
As a general instruction about road construction sites, I'd beg you people to remember that they are somebody's work place. Speeding or ignoring other signs on my site would be just like I decided to come sit on your office table, spilling coffee around and playing Stayin' Alive full volume from a portable radio. With the exception that our lives are in danger when people ignore signs. One week ago, I was nearly killed four times in two days.
I shall join in the beer conversation later on. I totally love beer, it's my favourite branch of culinarism, along with whiskey. Although wine is great, too!