Improving and measuring silverlight performance...

Seema shares some of her lessons learned towards  minimizing CPU usage in silverlight .. 
https://blogs.msdn.com/seema/archive/2007/08/09/silverlight-a-few-thoughts-on-minimizing-cpu-usage.aspx

I can vouch first hand for her first two as big winners...   There are some extra tips in the RC docs: 
https://msdn2.microsoft.com/en-us/library/bb693295.aspx

One last tip: test perf on both Mac and windows (Xp plus Vista). there are slight variations..

 If you have better tips.. please leave comments :)