I started using a nifty tool around a year ago call Rapportive. It works with Gmail.
Rapportive shows you information about your contacts — collected from social networking sites like LinkedIn.com and Facebook.com — adjacent to the body of their email message. If gives you at-a-glance visibility into their professional and social networking details, without requiring you to collect and/or look it up.
If you are a Gmail user, I suggest you install it. It is free. If you don’t use Gmail, I’m not familiar with any equivalents for other e-mail programs/services, though there may be some (add a comment below if you know of any good ones so that others can benefit from your experience!).
Rapportive summarizes it up like this:
We believe that companies will increasingly compete on treating people excellently.
How do you treat people excellently? You respond to people quickly. You help people feel like they belong. You personally connect with people: you care about who they are, what they think, and what they do.