Hey everyone,
I switched to this UI a few weeks ago for the first time, and really like it for the most part.  I can see why so many use it.  There were a couple things I wasn't super keen on, so I did a couple simple modifications.  This thread is really just to throw them out there and see if anyone else is interested.  I can send the files in response to PMs, or put something up in the technical discussion if enough are interested.  It's really just two small modifications:
1) The experience bar.  Previously the experience bar had the large and small bars to it, giving you about 5x5x5 or 125 ticks per level.  This gives you a resolution of greater than 0.8% (since you can also see increases of say half a tick).  The newer one does not have a decimal place (I'd read that it was actually impossible to add in a decimal), and just a single bar to it.  You can easily add back in the smaller bar, but then that doesn't have the smaller tick marks on it.
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My solution was to simply to add back in the old XP bar into the new player window. I did have to re-include the old image file in the new directory, but didn't do any modifications to it.  I also only did it for the player window, although it could be easily added into the inventory window aswell.
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2) The group window.  Perhaps I'm getting old and just can't see anymore, but I had problems seeing the small follow/invite and decline/disband buttons in the new group window.  I sometimes couldn't tell when someone had sent me an invite to group, or if I was the leader and could invite others, since the boxes were so small.
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Ungrouped / Invited / Disband pressed
My solution to this one was to increase the button sizes, and then add back in the same text that was there previously.  These buttons are a little kludgy, since I didn't want to have to adjust the image file (for instance, there's no text highlight like before when you mouse hover).  I just used pieces that were already there to try and get it to work.  I thought it turned out okay.
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Ungrouped / Invited / Disband pressed
Again, these aren't any big programming achievements.  They were pretty easy to do with notepad++ and a little bit of tinkering.  However, I'm just putting this out there for anyone who doesn't want to mess with the code and wants similar adjustments.
Note:  These might also be usable for Vert's UI (since they're very similar) but I haven't tested.