A good read about memory leaks in WPF and Silverlight. Most of the UI memory leaks are evolved around events registration with no unregistrating them which causes the GC not to collect objects.
Here are the main causes:
As developers we always strive to use the newest technologies and be kept up-to-date with our programming languages. The most terrible thing that could happen is to become obsolete with your skill, or that you are using an obsolete platform and Silverlight has just won the title. Its kind ‘a sad, but most likely, justified. Microsoft, again, waited for the final hour to pull the plug and still the enigma remains.
Earlier this month MS released Silverlight V3. It contains many many improvements over V2. You can read all about it in Scott Guthrie's blog. Personally I find the opportunity to run Silverlight as a desktop application appealing. If the technology will be able to proudly "hold" small to medium desktop applications, this will promote this technology several steps ahead.