It's bloody annoying to read, and makes you look like an uneducated idiot. It's also annoying seeing people get their "your, you're, their, they're, there" mixed up and then saying it doesn't matter because they're typing online. Well if you can't get it right online, you obviously don't ever get it right. What's so hard about typing one extra letter, it takes an extra half second (if you're really, really slow). What really, really, really annoys me is seeing people use absolutely pointless text speak, like 1nce, 2ce (I've actually seen this done before), and countless others.