Usually when I blog I do it in the morning before I head off to work. Every now and then I'll re-read something I posted in the morning and will edit the areas that I feel don't sound that great. I know a few people probably already read the post that I changed and will wonder why it sounds differently than it originally did. Do you think this is unprofessional? My blog is fairly new but I've managed to get a few people to the site.
I feel that it's much more professional then having typos or incorrect details. I wouldn't however, make significant changes to the overall tone of the post without leaving a note. Hell, by the time you read this comment, I'll have changed it 3 times. My blog gets an easy X,XXX hits on a bad day with many regulars and I've gotten positive response from readers with this policy.
usually after i make a post i change it at least 2 or 3 times after re-reading it and realizing what an idiot i am.. it's rare that i make a change after a day or so though..
I have gone back and updated, or changed articles that were a year old. Especially if they get a rush of new visitors because of current events or a mention in some other medium.
When I make a post sometimes I do edit as well, usually it is because I have forgotten to put information in the post that would be useful or helpful to someone else.
It doesn't matter if you edit it a hundred times, as long as you do what you say you are doing. Still to be on the safe side, you can download and use maxblogpress ping optimizer which makes your blog ping only when you make a new post and not when you edit it, thus, reducing the chance of search apis like technorati banning you for it (thinking you are doing it as a spammer which I am sure you are not.)
If it is minor edits -- spelling, etc. changing it is fine. If you are changing facts and/or other major points of your article, you should strikethrough the old sentences and add new, or write an addendum to your original article.