I found the command to show the version cat /etc/issue. I see at
Update paths - OLPC
that one person has experienced the loss of use for add ins, similar to my experience, after an upgrade to 656.
And now the proof, I am apparently now running 656 after I use the above command.
To the best of my knowledge I didn't do a update, so there must be an auto update "feature"built in to the XO. I'll dig around on the web for more info on this.
Alan