DataBuddy, Graffiti's data access engine, exposes a Query object allowing you to retrieve data from your site in almost any way you can think of. While the examples below are for Comment and Post, you can query almost any object in Graffiti - the list includes Category, Comment, Log, ObjectStore, PostStatistic, Post, Tag, User, and VersionStore.
Saving your data in Graffiti is easy. You can use ObjectManager from any code with a reference to Graffiti.Core. ObjectManager will store your object in the current database (regardless of database type), as long as it is serializable.