Yojimbo syncing is provided as a subscription service. The first 30 days are free, and the subscription charge is US$2.99 per month thereafter. You may cancel your subscription at any time; if you do, Yojimbo will simply stop synchronizing your data between your Macs — you won’t lose any of your stored information.
It’s an interesting decision. I haven’t found information about their plans for syncing with iOS. I guess we’ll see if customers are willing to start paying for syncing. They certainly are willing to do it for a ubiquitous service like Dropbox.