Sync to success

I love the cloud. It provides access to all my data from any device, any time from anywhere (and for anybody when the next security hole is discovered). No headaches about backup, storage and undelete. I'm on cloud 9.
Not so fast. When I need the service most it is down, the network is slow or latency is unbearable large. The cloud turns toxic. But I want my cake and eat it too. And yes it is possible. The secret is called sync (others call it cache mode). I only mostly want to interact with local apps and local data. These local apps send and receive data from the cloud as and when they have connectivity. They do that in the background, they don't bother me. The apps update themselves from the cloud if I permit it (individually or blanket permission). The apps are smart enough to figure out what data can be kept local based on context and device. To achieve that synchronization is king. There is still dust over the sync protocol battle. We have SyncML, CouchSync, NRPC, HTML5 sync, .net Sync, Expeditor sync and many others. Partial sync (what I would call " contentual sync) hasn't been solved satisfactory. What is your sync strategy?