Facebook is the fastest growing social network right now, and pretty much every major corporation has a facebook page, regardless of their business or whether they're B2C or B2B. So I don't think there's any problem with having a facebook page in terms of looking childish or unprofessional.
However, I wouldn't create a facebook page just to jump on the social media bandwagon. A facebook page requires regular updates to be effective. Otherwise, you may accrue some fans, but it won't actually do anything for you. The same goes for Twitter or any other social media site.
Also, don't treat social media as free adspace. People don't subscribe to a facebook page or follow a Twitter account just so they can get ads. SMM is about engaging customers in conversation to find out what your customers want, and also strengthen your brand by providing richer interaction.
A company that posts exclusive content, responds to fan comments, and gives free stuff on their facebook page will, not only gain lots more fans, but their brand will be a stronger presence in the minds of consumers than a company that just spams their facebook page fans or uses their facebook page as a billboard.