This looks amazing! First thing I realised after a few hours of Skyrim was that the UI svcked, it's great to see some people got the right idea about functionality.. I'm aware a few people weren't keen on the icons, but for what it's worth when I had a quick scan it took no time to figure out what category each one stood for, which I would consider most important. Thankfully it seems you've put a text prompt as to your currently selected category at the top too, which is handy. This seems most important to me as a gamer - function over form. It's a necessary evil due to the depth of RPGs that you spend a lot of time in menus, but a good menu system does all it can to reduce the time you spend in there. I don't really care how "Celtic" it looks (it's not Celtic anyway it's Nordic - the clue is in the name

), I want it to be readable, have clear and concise info, and be back out of it quickly so I can get back to whacking dragons with ****-off swords.

So far this really seems to have the goods.
Equipped items always at the top is definitely on everyone's list, if that's possible it would be excellent. I like the ability to sort by damage/weight/name/value/etc, that makes everyone's life a lot easier.
One thing I'd love to see is the pointer made er, a little less pointy - I'm SURE a lot of people's mouse-issues in menus are because the mouse pointer in skyrim is very long and sharp, yet gets hidden due to having a very similar colour to the menu background - this results in people misjudging, naturally thinking they're pointing to where the light-grey bit of the cursor is, when the point is actually well above it. Obviously there's a few other known issues but I don't think this helps.
I'm also unsure if you've done anything with containers yet, but the ability to sort items in containers the same as your inventory would be excellent, especially if you could see the contents of both at the same time. Also, make it impossible to consume/equip items from within a container - I know a few people who've chugged a boatload of potions by mistake because of this haha.
Slightly off-topic as well, but if you decide to work on the skills menu at all after this, I did a mock-up of what I thought would make a good skills interface a while back -
http://smg.photobucket.com/albums/v476/sane_man/?action=view¤t=ImprovedSkillScreen01.jpg
A few people on the thread at the time seemed impressed, but since I have precisely bugger all knowledge of flash programming I thought maybe you guys could make use of it, as an idea if nothing else.