I've worked for or in several businesses that use Linked In. It's not great for SEO, since I doubt the pages get indexed in any way, but it is a decent way to get noticed. If you're aggressive with blogging/social networking then your name will get around. It also depends on what your company does..
If you're planning a soft marketing campaign online it's usually a good idea to exhaust options, bearing in mind that only one may take off. There was an article in an old gotvmail newsletter (I use their advanced voicemail service), that mentions a few other sites. Might be a good place to start:
GotVMail Gary's Notepad - How-To - New Ways to Promote Your Business Online
Linked In is mentioned, as is Technorati, Youtube, Meetup, etc. All decent ideas to consider.