I am designing a Windows app that will get its data from webservices. It will also need to operate when not connected to the network. What options do I have with LLB for storing data offline? Is is a case of reading all EntityCollections needed and serializing to XML on disc, or is there a better way?

LLBLGen Pro objects are serializable. So LLBLGen is not a decision maker here, that's pure architecture decision.

I would have used a local db (SSCE... for example).