Just because it looks great and is readable on YOUR screen, doesn’t mean that’s the case for your viewers. I like to stick with 14-16 point text for emails and web, and about 28-32 for PowerPoint/Keynote presentations being viewed on large-screen HDTVs. Anything smaller and you run the risk of your carefully crafted text being unreadable. There are exceptions, of course—but I almost always stick with those sizes.
There’s actually a science behind the best font size for the web. There’s a lot of geeky gibberish in the article (which I personally found interesting), so if you don’t care about all that just scroll down to the bottom of the article and you’ll find a chart of recommended sizes for desktop, laptop, phone and TV viewing.