EDIT: Wording of 'dropping support' to 'dropping support for the legacy API'. Also added a link to the 1Password blog.
1Password dropped support for the legacy Dropbox sync API some time ago. I was a bit bogged as well, because it needed me to re-buy 1Password from the Appstore. Previously I had v3, v4 needed to be re-bought. When you were a user of 1Password v3, they made that very transparent and also wrote[1] about it on their blog
That sucked, _but_ I get why they did it. v3 used an API of DB that was legacy and they didn't want to support it anymore, because they had a new implementation around the corner which used iCloud.
And in my experience synching got improved a lot. Yes, re-buying sucks, but that's the developers choice. That's not related to iCloud at all. Plus, the new version works better for me, so kudos to 1Password to improving their product - and charging for it seems to work, I paid them lots of money and still am a happy customer(;
1. http://blog.agilebits.com/2013/08/08/1password-3-dropbox-syn...