I had a similar problem with the Facebook app. I downloaded the firmware update then tried the T4Two Free 'Pong' game which worked fine. I then downloaded the Facebook app, launched it and it started up then just closed, it kept doing this each time. I tried the T4Two game and this started doing the same thing!! (Even though it had been working initially). I was paniking like you, thinking I would loose alsorts of data or even that my iPod was corrupted or something (the recent news about the PS3 firmware update problems were in my mind). But I decided to try resyncing with my PC and as soon as I did that, the applications worked, although strangly I did have to delete and download the T4Two game again.
It has happended since (but thankfully only once) so there must be a bug with the Firmware, hopefully will be fixed soon.