Typos are fine, everyone has moments like that. What irks me is that every single person here born and bred in the UK spent at least 10 years being taught the basics of capital letters, full stops and sentences. They have absolutely no excuses for poor writing on here.
Fine, you don't get the use of colons or semi-colons, I can live with that. Missing the very basic of basics however is lazy to the point of contempt for your fellow forum users.
No-one's perfect (hell, check my posts and you'll often see an edited mark at the bottom), but it takes literally seconds just to double check what you've posted, and to make sure that it makes sense. There's very few people on here who have genuinely irritating posts these days, but the odd poster that slips through just makes me think they're rude.