Well, well, well. So Messages was indeed oh-so-quietly "done in" on Lion. It's almost spooky to have Apple capable of disabling an app you are using in good faith. Like a thief crept in during the night... But, since it WAS a beta, not surprising.
I didn't have an MBP before Messages beta was available, so I didn't realize it was originally part of the iChat app. So, finding it there now wasn't "new." It was, likely, the default location as in the past. The iChat thing is nowhere as convenient as Messages is/was.
I had the iPhone and iPad before getting the MBP 13. It surprised me how some things on the MBP parallel what you find on iDevices, but other things are totally not. Good thing I plan to upgrade to Mtn Lion. I expect much greater OS compatibility among MBP, iPad and iPhone with this in place - which I look forward to experiencing.
But, for now, I miss MBP Messages.