Well, it's been a ride in getting SSE ready for our upcoming beta.  Getting a server product to work in local data scenarios has been hard.  There are a lot of issues.  But, we're getting there.  

But Wow.  It is totally cool. 

All of the same APIs I use for full SQL work exactly the same for SSE.  But, I get Xcopy functionality on top.  So, moving the app around on machines that have SSE is seamless. 

I've been doing app building with SSE since early December for both Win and Web apps.  (Helping find the little issues here and there that need to get cleaned up.)  That's been fun since I am a self-described ASP idiot -- so I'm learning ASP along the way.  With both SSE and Cassinni, I can develop and play with local web apps that leverage  SQL Server to my heart's content.  I have to say that ASP's web developer product A.K.A. Venus makes web development pretty easy.  I have had an interesting time with some of the bugs ....

Wrt to Yag's post, I've also been using the new report control in the apps as well.  Works great.  In a demo I did for the Envision conference that's going on, I did a simple little form that uses the report control and Xcopied it with the .exe and the MDF to a different location to show it working.  Now, if I can just get the list elements in the report control to behave a little better ...