I recently got a note from a resume client who wanted me to look at the new online portfolio he had developed. It looked very attractive until I started reading! The tone was casual (sometimes flippant) and the content seemed aimed more at his friends than at potential managers. This is a young man who plans to use his website to help with his job search, and yet he hadn't really thought about his audience.
If you have an online portfolio or personal website and you give that URL to potential employers in emails or on your resume, make sure that it presents a professional image and that it sells your talents and abilities just as well as your resume does. If you are not a professional designer, pay a designer to create your site. If you're not a great copywriter, pay someone to write the content.
And, don't forget blogs. If you write a personal blog, don't write anything that you'd be ashamed for a potential employer to see. Remember that nothing on the Web is private ...your managers, peers, business rivals and potential employers could all be looking for you online. Make sure they like what they find!