Take the conversation option selection menu, for example: There's a white arrow on the left side, and the options are arranged in a column. It's designed for console players to page up and down through the options, then press a button when the arrow is beside the option they want. If PC players use WASD and Enter, it works much the same. If you try to select things with the mouse pointer, left mouse button and/or the scroll wheel, however, the option that actually gets selected when you scroll and click can be very dicey, even after patch 1.2. Before patch 1.2 (which also broke the arrow keys), it was even dicier.
Then there's crafting. Crafting with the mouse pointer and LMB is an inefficient mess, with Enchanting being the worst offender. Instead of being able to click every necessary option within a small portion of the screen, you have to click options on the left side, then either press Enter or move the mouse cursor way over to the right to click the Enter icon, then press R or move the cursor down to the bottom of the screen to click the R icon, then press Y or move the mouse cursor to the middle of the screen to click Yes. It's ridiculous — a single series of pop-up menus that you hardly have to move your mouse away from as you select options would be much easier and more efficient to use.
And then there's the inventory/trade interface. Trying to use the mouse, LMB, and/or scroll wheel works okay-ish, but it can be very wonky, and also fussy about where you click. You can quit the inventory menu accidentally by clicking too far to the left or right of a category, for example, even if the pointer is directly over a word. As well, on the PC, a grid layout (as shown in one of the many mock-up images) would be far better than a long, single-column list of categories and items. When PC players see those mock-ups, they say, "HOLY CRAP WHERE CAN I GET THAT!?" They say that because they know such a UI would be far superior to the current one.

