One of the things that has been missing in the Silverlight development story is a proper profiler that is simple to use and does not require you to hack the registry or do complex command line hacks to get it working. The Danish company called EQATEC has been making profilers for a while for the compact framework, but now they have implemented a Silverlight version that I must say I'm really impressed with. EQATEC has donated a professional license to the Balder project and I have already started using it, and my findings are very interesting. I've found more bottlenecks the last 24 hours than I have during the entire course of the project without a profiler. So I'm expecting Balder to get even more speedier in the near future.
If you want to have a look at how the profiler works, Channel 9 has a great video on it here.