If you are wanting to do anytime of networking, product reviews etc...then you must have a card. Say you ran into the HP rep and they are interested but you have no card so you're writing your info down on a piece of paper, not to professional huh.
Here are what mine look like. And this is an older design. My newer ones have my email which were not on the old ones...a big no-no!
I have a card for my professional blog site - The Writes Spot - as a Social Media Consultant. They can find links to all my other blogs there.
I get my cards at VistaPrint, which is very inexpensive. If you use one of their designs, make sure that you customize it as much as possible and remove the VistaPrint advertising on the back.
My card has my professional site's URL, email and phone numbers. I have versions with and without addresses. I use the address ones when I meet with people locally, but rarely since I work out of my home and don't want people just stopping by. I also have cards for my jobs with CafeMom and Mom Central, but use those less.
I do - I have a business card with my name, my address, a tagline and my social network info on the back. the card is the same design as the background of my site. the only thing I do not have on there is my phone number, but only because I don't necessarily want to put my actual phone number out there because of phone spam issues which is being a major problem as of late. If i do meet someone who I'd like a call from, I simply write it on the back - I designed a "white" space on the back of the card with no info so I can jot down any extra info. I always carry a think sharpie in my bag with me - and I always print my cards on matte paper, not the UV coated glossy ones (those are impossible to write on)
I get my cards from vistaprint.com and I pay the 10$ upgrade fee to not have the vistaprint.com logo on the back - but if you don't mind it, then I believe the cards are free.