I don't think this is to terribly difficult to do (famous last words) if you have SQL Server on your server and MSDE on the client machines. SQL Server supports replication, which enables you to synchronize the data on the client machines with data on the server, and vice-versa. So a user with a laptop running MSDE can disconnect from the server, makes changes to the data in MSDE while they're disconnected, then reconnect and synchronize the data. The synchronization works both ways: any changes the user makes to the MSDE data gets sent to the server, while any changes made on the server while the user was disconnected get sent to the MSDE database. Conflicts can occur when two users make changes to a record while one or both are disconnected from the server, but SQL Server gives you a way to handle that.

It was some years ago that I saw Gary DeWitt give a presentation at a conference on this with Visual FoxPro rather than .NET.

>We're developing a C# winforms application that talks to a MS SQL Server database. A requirement was made to have the application run "offline" (disconnected I suppose is another way to describe it?). We were able to make a fully functioning offline version using XML files for the offline data storage mechanism. This worked very well for a small database. Unfortunately, it chugged very slowly (almost unusable) for much larger data.
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>So my question is, what alternatives do we have to try to solve this speed issue? I've already thought of the obvious one (keep the offline data to an "acceptable minimum") but I'm looking for other ways :) We've been considering MSDE, however, the issue of synchronizing the offline data with the online/live SQL Server database remains. Is it "automagic"? What if the database was ORACLE instead? Does MSDE play fair with ORACLE?
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>TIA for any suggestions and/or comments.