I discussed a set of use cases not well supported by HTML5 ApplicationCache with the HTML WG during a breakout session at TPAC. These use cases were the basis for AtomDB are being solved by the DataCache API.
Found out that OMA and AT&T had similar ideas too. Also learnt that these techniques could be merged with HTTP caching.
Hixie agreed these use cases covered the ones the GMail team had asked for but he favored waiting until after AppCache had stabilized and browser implemented other HTML5 stuff.
I like to solve application problems using the Web (statelessness, hypermedia, self-descriptive representations, and uniform interfaces) to produce an asymptotically tight bound solution!