Social media is the bread and butter of customer relations management and there's no doubt that for companies, employees who communicate well online hold a certain cache.
Any personal blog or website you have could be owned by the boss and the trouble lies where personal and work collide and whether blogging takes place in the office or at home.
If your blog mentions company-related news, who owns the rights to it, will be difficult to ascertain. In theory, working for a prominent organisation and mentioning their developements within your personal site is treading on terra-infirma. Should the site become successful, things get even more complicated. Once revenue is involved who gets a share of the profits?