One of the big advantages of signing up with a professional networking website, particularly one that offers specialist areas, is that your clients are going to be people who were actively seeking you and your expertise. The other is SEO.
I've registered with tons, myself. The latest one is SkillPages, where I've had yet another opportunity to showcase my skills via the pictures I've been encouraged to upload. It's a networking site, primarily; the idea is to match you to people who are seeking your skills or vice versa. This is handy: I might need a cartoonist or someone who's good at Flash - I'm not.
Yes, there are other sites of this kind. I'm with them, too (Linked In, Guru.com, People Per Hour, Branch Out), but SkillPages is one of a growing number of info-cloning sites that allow you to import your basic information from Facebook and Linked In to save you the tedious work of uploading your name, address, and phone number, etc.
You can add your recent projects, but here's the twist: each time you mention the new design job/content writing project/etc., you have the opportunity to tweet it to your accounts on Twitter, Facebook and Linked In. That is dead handy! BranchOut and the other professional networking boards don't offer that. Linked In has a Twitter facility, but doesn't automatically post job or project details to it.
There are also opportunities to give and receive recommendations and to form circles of friends and associates for networking. Photo and video uploading is encouraged, and URLs are automatically linked.
The SEO advantages are huge: posting your URL on a popular website will boost your online profile and appear in search engine results whether they're do- follow links or not. Getting recommended by your connections there is as good as a testimonial. And the best thing about it? Unlike the bloated, lumpen, frustratingly slow BT Tradespace, SkillPages loads like greased lightning. I really can't recommend it enough.