Find Steam apps that you have in common with your friends, fast, so you're not wasting time asking, "What can we all play?".
Enter you and your friends' Steam "Vanity ID" or 64ID!
e.g.: http://steamcommunity.com/id/yourVanityID or http://steamcommunity.com/profiles/#your64ID#
If you do not have a "Vanity ID"
Open Steam. Go to the fourth option, STORE LIBARY COMMUNITY [YOUR STEAM-NAME] and mouse-over until you can click "Profile".
On this page select "Edit Profile" and find the field called "Custom URL" and come up with something awesome!