I hate email. I mean, I really hate it. When I'm managing a team, I think I'll set a three-times-a-day rule around email. I'll check it morning, noon, and night for a short period of time, but folks will need to use social media to look for a response. My reasons are as follows.
Transparency
This is the reason I'd prefer my staff to be on social media as well. I will only need to answer a question once. One post and your team knows what's up. The majority of interactions will be transparent. The expectation is both community building and efficiency. Because I can tag posts in social media, finding interactions is much easier there than in email. Yes, there are ways to use tagging in email, but the conversations aren't inherently transparent.
Accessibility
Many social media sites provide multiple opportunities for posting and multiple opportunities for receiving. You can set up some pretty intricate ways to get updates. Include getting an email message in that list.
SPAM
Yes, social media is known to have SPAM. Compare it to the number of junk email messages you get and they won't even compare. Have you ever signed up for a conference, a credit card, airline miles, shopping excursions, hotels, or anything else with your email address? Ugh.
Curb Appeal
The visual, verbal nature of social media will trump anything that email could ever deliver. Tumblr is my best example. All I need to do is scroll and click once in awhile to get the full visual effects of posts there. Sharing is easy too.
