Re: In the UK...
There's not a whole lot of difference on where you are, I don't think.
The things that irritate me the most (in no particular order) are as follows:
Driving in the left or middle lane of the motorway when the middle or right lanes are empty. I swear if there was a road with 17 lanes, Norwegians would still only use the left two lanes. (Overtaking on the right is technically illegal, but anyone who gives you a ticket would have to be a massive hypocrite for not also giving everyone else a ticket for not driving in the right-most lanes - which is also illegal.)
Not indicating at all, indicating halfway through, or indicating after the manoeuvre. Roundabouts are particularly bad here because Norwegian law recommends you indicate left when entering if you're turning left, but it's not mandatory so half the driving instructors say you should indicate, the other half say you shouldn't. As a result hardly anyone does.
Staying with roundabouts for a second: No roundabout exits are marked, so if you don't remember where you're going after you pass the sign warning you about the roundabout, you're fucked.
Incredibly slow driving. 5km under the speed limit isn't unusual. Until there's an opportunity for people to overtake - then you have to speed up as much as possible to limit the ability of anyone behind you to pass. Norwegians love to lead processions. If I could see through the red mist that regularly accompanies my commuting to work, I wouldn't be surprised if they're all wearing clown outfits too.
Part of the insistence on driving slowly could be due to the fact on non-major roads you have to give way to cars pulling out from the right. (I kid you not.) This is one of the more dangerous laws I've ever encountered anywhere. (I believe New Zealand has one that beats it, but that's another story.) So if you're driving on a minor road, anyone could pull right out in front of you without warning. Legally speaking, they have right of way - unless they're pulling out of a car park, private driveway, or they have signs directing them to give way (but you can't see those signs, so you'll never know). In my experience this tends to be more guesswork than actual knowledge as to who has right of way. (Major roads are marked with yellow diamond signs *after* intersections.)
Generally speaking the quality of the roads are pretty terrible and there are hardly any motorways outside of Oslo. (Most Norwegians driving to the far north of the country first drive east to Sweden and then head north.)
With all that said, I totally recommend seeing Norway. The scenery up the west coast is incredible. :) Just don't forget to re-mortgage your house before coming.