1) Company Image:
95% of selling and communication on the Internet is done by the written word.
Your website is your online business card. It presents you and your company to existing and potential clients. Just as when you meet a client face-to-face, you take care to be punctual, to make a good impression, to look tidy and to be ready to answer any question, and your website aims to do the same thing online. It should be polished, professional and informative. Spelling errors and poor grammar will make you look unprofessional and do not inspire potential clients to have confidence in you and your business.
2) Revenue:
Many consumers are wary of spam and phishing activity and a misspelt word could cause them to navigate away from your web page.
A survey carried out by FACT-Finder (the European market leader for on-site search and navigation in online shops), found that incorrect spelling and poor translations cost online shops 20% of their sales. It takes a lot to win over your clients, and very little to lose them; it is unforgivable to lose such a significant percentage of sales because of something that can so easily be remedied.
3) Search results:
Spelling mistakes can negatively effect the position of your web page in Google’s search results.
Matt Cutts, Head of Google’s Webspam team, has researched SEO issues in connection with grammar and spelling. In this video he explains that Google automatically ranks those pages that are free from mistakes more highly: http://www.youtube.com/watch?v=qoFf6Kn4K98
The Page Refinery 