Other niceness includes LibrarianSync or Collections Manager -- for managing collections in bulk, especially via a calibre plugin.
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Screensavers and collections are the main quality-of-life hacks for reading that I use.
But I also like having kterm (terminal emulator) available, under the hood the Kindle is a standard Linux box. Pretty much all the basic unix toolset is there, and USBNetwork lets me SSH into remote computers as well.
Yes, this is all useful at times. And if you are so inclined, you can repurpose your Kindle to do all kinds of interesting and totally non-ereader-related things. A bit like a Raspberry Pi, except it comes with an E-Ink screen.
Also, skipstone is a far better web browser than the Kindle's builtin "Experimental Browser". It does tabs and everything.
And it is nice to have a browser in a pinch.