The majority of mobile applications I build are on SQL Compact using Merge replication.    Merge replication although a little 'fun' to get your head around the first couple of times.   Once setup it up is really a remarkable bit of kit.

The ability to construct store and forward partially connected applications with the minimum (well by the time you've done it for the 3rd time) of fuss.

Seeing Click  last week I got thinking today about the one laptop per child project( http://www.laptop.org/ ),   3rd world mesh networks and other situations where low cost/low power and low bandwidth were all the order of the day; SQL compact and merge replication on Windows CE could be a great fit.

Producing applications that work sensibly with low bandwidth and low power is what Windows CE has been about for the last 11 years.   Plus I've still to do merge replication over a satellite link