This is pretty slick. The Database file sizes are small (Northwind = about 2MB), the assemblies to add to an application are small. It supports replication and a lot of other features. No stored procs, but it supports Views and full relational integrity. You can deploy it in a regular MSI project by simply adding the seven dll's and your database file.
Best of all, your System.Data.SqlCe namespace works exactly like the System.Data.SqlClient one. For example in a small Windows Forms test app:
private void Form1_Load(object sender, EventArgs e)
string cnstr=@"Data Source=C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf";
System.Data.SqlServerCe.SqlCeConnection cn = new SqlCeConnection(cnstr);
SqlCeCommand cmd = new SqlCeCommand("select * from employees",cn);
SqlCeDataAdapter da = new SqlCeDataAdapter(cmd);
DataSet ds = new DataSet();
-- and you get this:
One of the most important selling points that astute developers will recognize here is that you can run the ADO.NET Entity Framework (which in my opinion, at BETA 3, is getting to look quite mature) against a Compact Edition 3.5 Database and use the same program/application against any back-end (assuming the database schema is same), you have to just modify connection strings.
I heard that Janet Leverling went to work for Google. (That's a joke, she really took all that MSFT stock and retired in Costa Rica).
Here's the bits: