Your About page is where you get to define who you are and what is at the core of your work and thoughts. If you are doing creative media, especially journalism, your About page should also be the place where you disclose anything that might be (or be perceived as) a conflict of interest, though of course you should also disclose that in any postings you make about relevant topics, as noted earlier.
If you have a resume or CV, link to it from the About page, both as a downloadable PDF file and a Web-readable HTML file. If you give talks, consider posting your speaking calendar (for privacy and security reasons, some people don’t do this).
You should always include a way for others to contact you. You can create a Web form for them to fill out, or you can provide an embedded email address and phone number, or you can do all of these things. You should also have a Contact link on your home page, and ideally on all pages via a menu at the top.
I don’t change my About page very often, and you probably won’t, either. Minor tweaks, yes, but this isn’t the place for discussing every quarter-turn of the screw in your career or other goings-on. Define yourself here in the broadest terms. Blog the smaller stuff.