You can't just put nodes in different regions, even with a database like MongoDB. It will work in theory, in practice you'll have all kinds of latency problems.

WAN replication is a hard problem and glossing over it by waving your hands is a disservice to readers.

"Real" solutions are to run a database that is tolerant of partitioning, and have application level code to resolve the inevitable conflicts. Riak, Cassandra and other Dynamo inspired projects offer this. On the other hand you can use a more consistent store and hide the latency with write-through caching (this is how Facebook does it with memcached + MySQL), but now you have application code that deals with managing this cache.

Either way you have to have very specific application code to handle these scenarios, and you may even run a combination of solutions for different types of data you need to store. There is no silver bullet, there is no framework or product that does it for you.