It would all depend on the circumstances in which people find themselves, both as far as their available time and the amount of income they're generating from the site(s) or business they are promoting. If they are social media savvy and enjoy updating their Facebook fan page(s) and interacting with fans, then by all means they should do so.
If it becomes too time consuming and/or they don't have the skills to engage effectively with social media -- and obviously Facebook in particular -- hiring someone is a great option. They would have to be very careful, however, as it's got to be someone who is reputable and can be trusted.
That's the crucial factor for me. It would have to be someone who is trustworthy and has high standards and is dedicated, and above all, does not do anything that's injurious. There have been reports of companies who have had people posting to social media on their behalf who have done so recklessly, and they wind up having to do a lot of damage control.
I would try to find such a person through referrals, first of all. If that's not possible, I would do a lot of due diligence before hiring someone. I would also give them a probationary period and monitor their activity and make sure they are posting in a way that best represents the brand/company or Web site.