Hmm. I'm not quite sure what happened. I seem to have two LaunchPad accounts. Not even sure how to get back to the cmcwerner one.
In any case, I ended up logging into LaunchPad with a different account, added the public key to that one and now the command
bzr checkout --lightweight -r 2247 lp:~mdipierro/web2py/devel web2py
(Sorry about the early post with an incomplete message. Not sure how that got sent out.)