I was recently considering using GoogleData for a hobby project to store my service's old data, (say 24+hours old), while I keep the fresh data on my servers (hobby project==cheap home server).
However I haven't really heard of anyone using GoogleData, so I was wondering about what other's experiences have been.
Edit: My brief usage pattern would be to basically store (cached versions) of objects representing (historical) entities. And relatively immutable data like past events or these entities, global prototype data my objects (also relatively immutable), in order to reduce the load on my server.
As for active entities I'd be storing changes locally and then posting them to GooglData (after 24 hours).
Thanks
Since you didn't really get a satisfactory answer to this, I might suggest looking at Amazon SimpleDB. It's not free, but unless you're storing zillions of records you'll probably only spend pennies per month. Like Amazon's other web services, you only pay for what you use.
SimpleDB is more generic than the Google Data services, which may suit a wider range of applications.