Joel Pobar (master of all things dynamic) wrote a great piece on reflection in this month’s MSDN Mag..
Reflection: Dodge Common Performance Pitfalls to Craft Speedy Applications
He does a good job spelling out where to use (and not use reflection), what the perf implications of reflection are… some good stuff on CLR 2.0 as well.
As an aside, much of this information was gathered and distilled as of an exercise the Windows team strongly encouraged us to do such that they could make wise judgments about where to use reflection as part of code the ships in Windows. Kudos to Joel for pushing this process all the way through to the end by getting the information out to you!