¶Flat buttons vs. 3D look
The current trend in user interfaces is to eliminate 3D borders and make everything look flat, especially buttons.
When I first started using UIs that had the 3D look, I loved it because it gave visual cues as to what could be interacted with and what was a container. Raised objects were things you could drag or twiddle. Impressed areas grouped things or could accept things. Flat objects were static indicators. Sure, there were people who overdid it and made their UI look like an obstacle course, but for the well designed UIs I thought it made a huge difference.
The trend now is to eliminate all of the borders and leave just the text or icon. The main argument is that it's visually cleaner, but to me, it makes it really hard to tell what you can and can't interact with. If you're lucky, the person who designed it at least used controls that show borders when you mouse over them. Otherwise, you have to click all over the window like an idiot, trying to figure out which of the icons do something and whether they do something different than the nearby widgets and text. It makes me feel like I'm playing an old LucasArts adventure, mousing everywhere trying to find some object in the dark cave that I can light to get to the two-headed squirrel.