We are using Sqlite for server side saving. We wanted to use a database driven system and MySql seemed like the obvious choice, however, we didn't want to add any additional requirements or setup procedures for using the engine. Sqlite is fairly similar to MySql in syntax so switching between the two won't be very difficult for anyone who knows what they're doing. (Ie: Anyone who would design web administration, web markets, vip systems, automatic account updates, donation management, etc)