Diablo – Where do recently played with people show up

To find out how long you've played a certain character, when you're on the character selection screen, select a given character. It says on the right how long you've played them:

You can also find out how long you've played a class. When you're on the screen just after the character selection screen (the one from which you start a game, change quest, etc), press P to bring up your profile.

You'll see a screen that looks like this:

Hover over the class to bring up a tooltip for how long you've played it.

After several days worth of research, using the items offered at the Auction House as a guideline, I was able to determine that socketed items are generally available as low as level 15. It does not seem to matter what item is in question (armor, rings, weapons, etc) - you must be level 15 to equip something that contains a socket.