Life's too short...
In this increasingly mobile, on-the-go, world, when people are reading on commuter trains, or grabbing moments at a stop light, running from parking lot, to elevator, to office cube, etc.... many on their mobile phones, and "misteaks" with fat fingers happen. Not to mention auto-correction on-the-fly -- that doesn't always get it right.
I do agree, repeated and error laden posts can influence your perception of someone's intelligence. However, I think this forum is full of incredibly brilliant and extremely thoughtful members, who do spend time thinking about their posts before they hit "Post Quick Reply". Not all of us aced "are" grammar classes, but we did ace finance, engineering, software development, chemistry, medicine, etc., etc.
... and so I'm okay with the occasional hit send, before rereading your entry 3+ times, checking for errors, errors. It's the thought that counts.