Where is Shuffle feature in Itunes 11 or how do I downgrade back to Itunes 10?

Select (highlight) the chosen Playlist and click on the Shuffle icon:

and a random song from that Playlist begins playing, and the Shuffle icon in the Now Playing window (which up until then had been blank) will be in blue:

and if you click on the Next list, you will see that the next songs to play are a shuffled set from that Playlist;

Of course!

Either:

• While a song is playing, press the Select (centre) button three times. You will see the "choose shuffle" option. Simply scroll the wheel to either Songs or Albums and press the Select button to activate it. You will then see the Shuffle icon in the top right of the screen. Or -
• While the iPod is not playing anything, you can still turn on the Shuffle option. Go to Settings/Shuffle and each time you press the Select button, it will toggle the Shuffle between Off, Songs & Albums. Choose the option you want. Then navigate to the Plylist you want, but instead of entering the list, simply highlight the Playlist name and press the Play button. The iPod will chosoe a song from that Playtlist at random and then continue to play the remainder of that Playlist.

You may notice an option on the Main Menu and the Music Menu for Shuffle. (It may not be on there, it can be turned off.) Be aware that this particular choice will simply start Shuffle from "a song on the iPod", not from a specific Playlist. Use the methods above to play from a specific Playlist.