What are the most under-appreciated Editor / IDE features?

I like the ability to find files/resources using a popup incremental search dialog rather than hunting for them in a conventional project treeview, which takes me ages. For example ctrl-shift-r in Eclipse, or alt-shift-o in Netbeans. This is how I open files 90% of the time when working on Java projects at work.

The ability to select code structurally. For example, select the function I am in, the current div, the current for-loop etc. Very helpful when working with long, deeply nested html files. It's horrible trying to eyeball the closing tag of a nested div while you are trying to drag-select it over several pages.

I love any feature that insulates me from project configuration and the build process and lets me focus on coding.

As much as it is loathed, I miss Visual Studios’* ability to drag and drop widgets on to a form then being able to click that widget and assign an on event. Being able to freely draw what ever I needed (and worry about the code later) allowed me to design a work-flow that was unsurpassed.

*Circa VB6

Built in terminal. Every single one I use has gotcha's to the point where I now use vim because the actual terminal is more handy.

Even if you have gone through the time when saving often was the norm, and know what you’re ‘missing’: not crashing seemingly randomly.

Multiple cursors