I emailed Landware's support -- got this response:
Please visit
http://www.landware.com/wm5/ for the current status of Windows Mobile 5 compatibility.
There's an update there which I downloaded an installed (about 5 minutes ago) and it synched (loaded my accounts)! It puts a new user ID, so I just contacted them for a new activation code. Haven't had time to put it through the paces yet, but so far so good. They're also requesting feedback about new upgrade -- so apparently it's a work in progress -- but at least there's progress!