Data synchronization

[Alex Shaw]

Hi

Been researching various data synchronization techniques.. and these are 
the ones I've found most interesting:

1. Google's Map/Reduce (not really data synchronization but still 
interesting)
http://en.wikipedia.org/wiki/MapReduce

2. SyncML Protocol
http://www.openmobilealliance.org/release_program/ds_v12.html
http://en.wikipedia.org/wiki/SyncML

3. CouchDB
http://couchdb.org
http://blog.leetsoft.com/2007/9/2/futuretalk-couchdb

A slashdot article 
(http://ask.slashdot.org/askslashdot/07/08/27/2359245.shtml) even 
suggests rsync.

A process I'm working on involves 3 simple steps:
1. Laptop <- Pull changes since last connection.
2. Merge local changes.
3. Laptop -> Push changes back to central server.

I'm leaning towards a CouchDB approach but using a modified version of 
Andre's RevOnRockets server using Valentina (mainly for the encyption 
but may use sqlite and a VPN like hamachi) and a XML protocol (instead 
of JSON).

Has anyone had any experience with this subject and has some useful 
suggestions?

regards
alex