One of the keys to being successful in the marketplace is to be findable. For many companies that translates into trying to be everywhere. It speaks to the old broadcasting mentality of filling every empty minute, space and sound wave with messages. And so companies have presences on Facebook, Twitter, YouTube, Flickr, LinkedIn, Foursquare and and and. Mostly coupled with a weak infrastructure to support all these platforms, presences and initiatives.
These unfocused efforts often lead to deserted fad islands and empty bandwagons.
It’s more valuable to each stakeholder to identify first where your audience is and will be in the future. Join them in the best way you can. Take a long, hard look at your real capacity to add value to a platform. If all you be is mediocre, stay away. Build your infrastructure first and then join your audience. Not the other way around.
Your marketing shouldn’t be run by Google and SEO lords whispering in your ear to build more and more places and links. Your marketing should be run by the desire to provide something special and valuable.
uwehook 
Well said. Couldn’t it be argued though that a presence of Facebook, LinkedIn, Twitter, (especially those 3) is required to some extent because customers may come looking for you there?
Not in every case. Is it really necessary for a household cleaner to have a page on Facebook? Or is there anyone interested in a Twitter feed from a toilet paper manufacturer? Charmin invested instead in the SitorSquat application. Much better way of delivering value. In addition, it might be more effective to build a mini-community in working with new apps (Instagram as an example, could be a great opportunity for a community of like-minded) and not just pull the lazy Facebook card immediately.