I'd only been using this plugin for a short while, but fell in love with it right away, mostly because of the CSS validation that the custom CSS editor does as you're entering your CSS. Sometimes it made some incorrect suggestions, like removing some qualifiers that I really needed to increase the specificity of my selector (luckily I knew enough CSS to be able to confidently ignore those suggestions).
However, my love turned to annoyance when I discovered that entering CSS into the "Standard" stylesheet (i.e., the one for non-mobile devices) didn't get imported into mobile devices. That is, this plugin has two different style sheets, one for mobile devices and the other for non-mobile devices (which is referred to as "standard"). You select between the two by clicking one of two links to the right of the Lazyest Stylesheet option page.
Let's say you want to change the font-family of the body element (i.e., the default font-family for the whole site). You enter the CSS rule into the standard stylesheet, and everything looks good on your desktop machine, but when you go to your smartphone, you notice that the site still displays the old font. That's because you have to switch over to the mobile stylesheet and enter the rule over there as well. And clicking on the checkbox that says to disable the mobile spreadsheet won't cause the standard spreadsheet to be imported in its place (I was hopeful, but disappointed).
I'm not sure why this was designed this way, perhaps the developer wanted to not burden the user with having to code media queries, but it's very annoying to those who do know how to use media queries, having to replicate CSS between two different fields. My suggestion would be to do away with the mobile stylesheet (probably difficult to do since someone out there may be using it) or add an option to import in the standard stylesheet on mobile devices.