The menu command "Go to Current Song" (in the Controls menu of iTunes 11) indeed shows the playlist that the current song is playing from, but it does not select the current playing track. The Command-L keyboard shortcut no longer works either. Looking for an AppleScript workaround, I found that reveal current track behaves the same way. The reveal command still selects a playlist, eg: reveal current playlist.
Update: Apparently these fails happen when a song is playing from a playlist but it's OK when a track is playing in the Music library.
Update 2: Here's a script that will reveal the current song in the Music playlist no matter where it is playing. Be sure to give it a shortcut.
tell application "iTunes"
set dbid to (get database ID of current track)
set musicLib to some playlist whose special kind is Music
set theTrack to some track of musicLib whose database ID is dbid
Obviously, this doesn't help get you back to the current playlist. But if you need to access the playing track for some other reason then it'll do. You can always right-click the LCD and access the current track's Get Info, Show in Playlist, and so on.
Update 3: Kirk has an important observation on this issue.
Update 4 (December 16): This appears to be fixed in iTunes 11.0.1.