Are you wanting the geometry and attributes for a gis purpose or just to save them for the user in a more permanent form than local storage?
If it's the latter, I suggest using php and mysql to store and retrieve data. I use them so users can save maps, graphics, bookmarks and more. This approach does require some form of authentication for the application. The basic concept involves using dojo's xhrGet, xhrPost, toJson and fromJson on the front-end, and php (php has great json capabilities) & mysql on the back-end. Serialize objects with dojo on the front-end, post and save on the back-end. Retrieve them as needed and use the returned information to return a map to a previous state, recreate graphics, etc. In my opinion it's easier and more functional for such things. One of my newest features (the client who's testing it for me in their application loves it) is the ability to move and size the regions (i.e. map, controls, toolbar, etc) just like ArcMap. Not only is the map, it's layer state and user graphics just as it was last time they used it, so is the individual user's preferred layout of the application. It sounds like you have access to AGS, but it is possible to build a GIS data store with mysql. Mysql does have geometry field types. The JSAPI can be used to add feature layers, query, find, identify, etc from any url that returns json in the proper format. I've even seen dynamic layers returned with php and mysql; albeit slow and graphically unappealing.
That's my broad, non-technical take. If it's of no help, my apologies; but whatever your goal and however you end up there, good luck.
