I posted a ticket about this but them rated the response and I didn't realize that closed the ticket. I've tried everything recommended and they still don't show up. The sync log does show them downloading, but they never show up in the interface. I've forced, I've purged, I've turned off filters, etc.. no luck. I noticed someone else on the app store comments have the same problem..
I have the same problem on iPad and iPhone. Folders still show, but all say zero tasks. The Google gadget shows the tasks correctly as before. Even stranger, if I add a task on the iPad, it appears in the Google gadget list but it is STILL not visible on the iPad itself!
OK, so looking through the news forum I saw that deleting the app and re-installing has solved the "tasks not showing" problem for some people and it has for me too. That's a relief!
It doesn't appear to be a very common problem, but note that I had the same issue on two separate devices: iPad_1 (iOS 5) and iPhone 4s (iOS 6) so it looks as though it is something to do with the account rather than the device/OS. As an aside, when changing settings within the iPad app, the first change causes the settings screen to get scrambled, and it flies off the right side of the screen. leaving and returning (to settings) lets me do more, but it does look like a little fix is needed there too :-)