Have you or your clients made any (or all) of these 3 social media mistakes

I was reading some interesting articles about social media mistakes and the three that seem to be talked about the most are:

1. Not every company needs a big presence
2. Over-investment rather than simplicity and keeping nimble
3. Believing that the SM efforts must be tied into existing IT infrastructure rather than creating something new or keeping it simple

The last one is a back-end issue that can impact the members and subscribers of your social media presence. But in terms of the first two, I am curious to know if anyone has had a client or has worked for a company that was guilty of either or both?