As more and more people are doing more and more social networking, the lines between work and play, home and office, are blurring. I've got coworkers and friends on Facebook. I've got coworkers and friends on LinkedIn. I follow both business contacts and old university friends on Twitter.
Being aware of your personal online brand is important. It's important for you, and it's important for the company you work for. For example, if you post something like, "I hate my company! It sucks!" Well, when someone finds that, you look bad, and your company looks bad. Nobody wins. (Except for your company's competitors, but they won't want to hire you now.)
The thing about the Internet is that what you say just kinda sticks. That random comment you made in 10 seconds way back over a year ago is still there, ready to be quoted word for word.
That being said, here are: 50 Tips to Brand Yourself Online
I would say that the biggest "tip" I can add is, overall, be active. Stay in control of your personal brand online. The more you're actively branding yourself, the less significant all that other stuff will be. If you're an e-commerce specialist and you also really enjoy Lord of the Rings, what do you really want business contacts to see? Well, you may post on a few forums related to your love of Tolkien, but those posts don't help you in the business world, so you need to balance those off with posts related to what you do at work. Tweet about e-commerce sometimes (but make it interesting, obviously). Answer a few questions on LinkedIn. Comment on blogs. Or, heck, guest post on a blog. Just make sure that when I Google your name I find something that really positively sells who you are and what you do.
Now, for some, that will be a tonne of stuff related to Lord of the Rings more than "e-commerce" (or something else stereotypically "business-y"). The point is to be in control, and to that end, active.