Some good points here, however I blog for fun as much as other people's entertainment, so I don't mind if the odd typo slips through. I'd also not mind reading a piece on here with the odd typo, for me it's all about the content.
Having said that, I have a business blog too which is business focused so your points are all very valid for that, and I've used proof readers before for books I've published. I guess it's down to how well you type, your command of English and who your audience is.