I found White Smoke to be the best online grammar checker software available. I've been blogging for five hours everyday for a year now. Grammar has never come easy for me and I tended to waste a lot of time triple checking my articles. Before I paid for WhiteSmoke, I tried some free online grammar checkers like grammarly.com and spellcheckplus.com. I had both free online grammar checkers check the same sentence for error and found different results. I also noticed the free grammar checkers missing errors I created on purpose. When I did eventually pay for White Smoke, the results were impressive. I did notice misplaced commas, and a few glitches, but it was by far better at checking grammar and quicker/easier to use.

Bad grammar on a blog or website can have significant negatives affects

1. People may not may trust that what you're saying is true if you can't even write.
2. They are less likely to 'Like' or 'plus' your page.
3. Google notices bad grammar and there's a strong change it may effect your search engine ranking negatively.
4. You may miss potential 'long tail keywords' or important keyword phrases, because you used improper grammar.

If you intend to do some serious blogging, you'll be posting 3-5 times a day. It wouldn't be realistic to go back and correct hundreds of articles. If you want to go pro blogger, I would recommend investing in a grammar checker in the beginning.