Yes the Silverlight client has some perf issues you should be aware of. If you haven't seen it, check this out: http://blogs.msdn.com/b/rmattsampson/archive/2012/12/28/lightswitch-performance-tweaks-anyone-can-do.aspx
We did optimize what's sent down the wire in VS2013:http://blogs.msdn.com/b/visualstudio/archive/2013/10/09/lightswitch-performance-win-in-visual-studio-2013.aspx
And we also did address a bunch of design-time perf in the March tools update so make sure you have that installed. http://aka.ms/officedevtoolsforvs2013
Going forward we're seeing customers ask for mobile and better business & data services support so this is why have been working on HTML5 and Office 365. I should mention that the above talk was really well received at BUILD.
Thanks all that came! It was a really fun session.