One-stroke Focus button for timeline, like in Avid
This is a feature I use all the time in Avid - it's called Focus and it zooms in to the one frame level on the timeline, centering the frame you are viewing. When you hit Focus again it zooms back out to whatever level you were at before zooming in and remains centered. I like the zoom all the way out feature of Final Cut (shift+Z) but really miss the zoom in feature.
For example, you're watching your sequence, you have the timeline set so that you can see three or four minutes of footage there, and you realize you need to trim a few frames in the middle. You need to carefully select which side to trim on each track, so you need to zoom in to do that. In Avid you would hit one button and you're there. In FCP it looks like I have to hold down option and hit the "-" key several times to get to the same place, and then I have to do the same thing to get back to where I was.
It may not sound like a big deal but it does put a lot more strain on the hands and wrists, over time.
This focus feature is also great for trimming. I like to set avid to automatically focus the timeline when I enter trim mode.