I have finally gotten around to installing Rapportive. Something was so obvious, though, that I failed to notice it is that it's an add-on to your browser. Meaning if you install it on your home computer, it will only latch itself to your browser on that computer. My office computer required an installation as well. This is not really a biggie, just an observation I wanted to point out.
I also realized that majority of the people I converse with by email are not my contacts at Facebook. Now that's interesting. Although there is also the possibility of my friends using different email addresses, hence the system is not able to correlate my Facebook / Twitter friends with my Gmail correspondences. Barring Facebook / Twitter updates, Rapportive shows you their most recent emails to you instead.
At any rate, I think Rapportive is a good way of checking how you are linked with others, and it's a great at-a-glance notification of their statuses.
Give it a try. It's fast and free. http://rapportive.com/