What concerns should businesses have about having a social media presence?

Pick and choose your platforms carefully. If you're a B2B business specializing in refurbishing computers, you probably don't need a Tumblr account. However, if you're in a creative industry, it's assumed that you would.

Sure there are a few downsides:
Social media can be a time suck unless you stay focused.

You need to monitor it so you see when there are conversations about you, your brand or your industry so you can get engaged with them.

Somebody does need to be in charge so the corporate messaging stays clear.

You want to be real and personable, not salesly and pitching your product. If that's not you find someone in your company who can be the voice of your brand.

Even if you don't speak yet, listen. If you are a business to business corp you have an incredible opportunity to observe your customers and what they say about the products you offer and your competitors in the wild. Think of it as an un-encumbered focus group you don't have to pay for.

As for Gail's customer service comment. You don't make offers to one user you're not going to give to everybody, this is a public forum. Connect with people privately if you must.
But don't make the mistake of avoiding social because people might complain about you. They probably are. You can stick your head in the sand and pretend your customers aren't complaining or you can see a complaint as an opportunity to correct a problem, identify a mis-perception and give the proper information.

Yes, you need to have policies in place to deal with a complaint on social media, and then you need to act before it takes off like wildfire and you can't fix the problem.

Being present and on top of a situation ends up making you look like a winner.

Longevity and dedication are required in order to be successful in Social Media. A lot of time can be wasted if you are not prepared for this upfront. All too often people give up after not seeing results they expected. Don't set your expectations too high and have a direction with your efforts.

I strongly recommend hiring a professional to help your business achieve recognition in Social Media. There is a method to the madness and it varies from business to business.

The major concerns are
the choice of target audience
the choice of appropriate message and media channels
goal setting
planning annd prioretizing of social media activity

Some excellent answers here! I'd add consistency to the list. Once a business makes an appearance in social media, users and potentially consumers will expect that the account will be kept current and be relatively active.

The foundation for being consistent is creating goals for your social media efforts, and a plan in place to guide you (as you would with any kind of marketing activity).

My number 1 piece of advice with regard to social media marketing is that you make sure your efforts are MEASURABLE.

As has already been mentioned, social media marketing can be extremely time consuming, and if you do not have a dedicated resource to do it for you, I would strongly recommend a tool such as HubSpot which allows you to quickly jump into relevant conversations related to your services, offer helpful advice, suggest a follow up call, and monitor which social media channels you spend time on yield the most leads and new business for your organisation.

All of this can be done from the easy-to-use HubSpot dashboard, where you can view graphs and reports on which conversations you joined, which led to leads and new business, and therefore, where you should continue to spend your valuable time.

I am a certified HubSpot reseller and administrator, so happy to discuss this in more detail with anyone who is interested in learning more about HubSpot or social media marketing in general (sandygans@gmail.com).