You can really use CouchDB on Android.
Here is a video discussing CouchDB http://www.youtube.com/watch?v=3RdcKWYGqig
You will need an external SD card. It works as a service, so you can use multiple applications using CouchDB. It also has amazing replication capabilities. Therefore, if you need to synchronize with the main database, then COuchDB makes it very simple.
There is more details in this answer fooobar.com/questions/283669 / ...
There are also several tutorials on the Internet, but for starters you can download the CouchDB app from the Android Marketplace.
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