I noticed a lot of the questions in here are about tweaking your theme's CSS - changing font sizes, element positioning, et al. So I wrote a quick guide with examples about how to make those tweaks safely and without too much hassle. You can read it here.
And, at least for the next few days, I would be happy to answer any specific questions anyone has about their shop's CSS. If you want to make a tweak to your shop, but you're not sure the exact CSS to use, ask away and I'll do my best to help out.