Ask HN: Syncing data with a central service across WEB

Scenario: I'm building a WEB service that provides service to various clients. In the next step I would like to integrate my service with clients' existing data, making it necessary to synchronize data bidirectionally (both ends can create or update data).

Since I am very proficient in CouchDB (Lotus Domino) architectural model, my first thought was to use CouchDB pull replication to pump the data back and forth.

I'd like to know, what is the obvious solution/alternative to my proposed approach. Message queues? Polling the central service, while maintaining local cache?

Requirements:

>Installation considerations and ease of use are primary concerns,

>The proposed method should be tolerant to connectivity issues enabling the clients to work offline,

>Data volumes are going to be low (10's of megabytes per day, max),

>latencies are not an issue, 15 minutes is entirely acceptable.