*Sidenote: wish I knew a little more about .xsl coding because I'd love to be able to change a few things about the stylesheet.
It's not too difficult if you're willing to put in some time with web-based tutorials and references. There are some XSL-specific editing GUIs, but I have found Notepad++ to be more than enough for me.
XSL is not a procedural language, so it takes a bit of getting used to. Forget about modifying variables on the fly or calling functions - it took me a while to wrap my head around how it works.
O'Reilly's book is a good reference. There are a handful of online resources, and of course stackexchange has a tone of already-answered questions.
If you have the time and enjoy the challenge, I think it's worthwhile. I've created several stylesheets that save ten minutes here, half an hour there, sometimes more, every time they are used. Doesn't seem like much, but adds up over time, especially with lots of user implementing it on a daily basis.