I purchased the new version of 1Password earlier today and installed it on both my iPad and iPhone, setting up the sync via both iCloud and Dropbox as I hadn't yet decided which to use. Upon doing so, the app would consistently freeze after the unlock screen with the settings icon animated in the bottom right corner. I assumed this was due to some kind of sync error, and confirmed that upon disabling "Documents & Data" for iCloud, the app would resume full functionality.
Not only that, but if at any time, the "Documents & Data" option in iCloud was turned back on, it would once again freeze -even if iCloud sync is disabled within the app-. The only way to turn it back on without causing a crash is to go into Settings > iCloud > Storage & Backup > Manage Storage and then hit Edit and delete the "onepassword" entry.
I'm currently sticking with just Dropbox sync as it covers more platforms anyway, but it took me a little while to figure out the problem and was on the verge of leaving bad feedback on the App Store before I solved it. I thought I'd do the right thing and let you know before those 1-star ratings start appearing!