I'm really impressed and super happy with the new CSS module. It's made adding custom CSS a lot more convenient and a lot less stressful. I especially like the color coding, and the ability to select and replace text in multiple locations at once. It's a dream, for someone like me.
However, I've also been extremely frustrated by two things, which I consider to be bugs:
(1) I tried commenting out a section of code that I thought I would use later. When I clicked "Save Stylesheet", the comment disappeared, and my work was lost.
(2) I tried using -webkit-filter, which worked fine in the theme's stylesheet. When I saved, however, it was deleted. I don't know why Jetpack would delete perfectly valid code.
I do appreciate how it cleans up and auto-indents the code, and I have to say, I fully intend to use it in the future, and maybe even for themes that have custom CSS options. However, it seems to be a little over-zealous in its current implementation, and I'd appreciate being able to save my comments and "new" code.