The Reaper blog just published a post about a setting I didn't know about, and it really helps me a lot! It's called the "Snap Relative to Grid" setting.
In a lot of my tutorials, I warn people to pay attention to whether the Snap tool (looks like a magnet - see the pic on the left) is enabled or disabled. It's incredibly useful when you want to snap the edges of your item to a gridline (which can be bars/beats, or minutes/seconds, etc.). But if you are trying to nudge something just a bit to the left or right on a track, having the Snap tool enabled will be trouble.
One problem I run into quite a bit is when I am dragging a bit of audio from one track to another. I don't have a very steady hand (so you don't want me doing brain surgery on you :)), so I almost always manage to slip the audio a bit left or right when I am just trying to drag it up or down.
Of course, this will mess up the timing, and I often find myself undoing ("ctrl-z" is the best keyboard shortcut EVER) and trying again. Or I drag the edge of the audio item out beyond its actual start or stop time to get it to line up with a gridline, then turn on the Snap tool, then drag it up, then turn off the Snap tool. Craziness, I know!
In my mind, I knew there was a way to keep the audio aligned in time while dragging to a different track, but I'm lazy, so I never looked it up.
Well, it turns out the answer is "Snap Relative to Grid." You just go to the Snap/Grid settings (right-mouse click on the Snap tool) and put a check mark in the "Snap relative to Grid" box. That way, if the edges of your audio happen to fall between gridlines, and you want to drag the audio up to a different track, the edges will stay aligned with however far away the audio was from the nearest gridline to start with.
In a nutshell, this means you can drag your audio clip up to a different track without worrying about it slipping left or right (earlier or later in time) in the process. In other words, it's the right tool for the job I've been doing the hard way for years. Yay!
Here is Reaper's blog post about it, along with an animation that shows you both how to select the option and what it does for your audio item when dragging it up or down to a different track. Hope this makes you as happy as it makes me :).