Advice Weaving in AspectJ
By Eric Hilsdale and Jim Hugunin. Interesting to understand how weaving is implemented. Also the articles has an excellent section about performance, which is very easy to understand after you have understood how weaving is implemented. In short: avoid reflection, which can cause a 2900% overhead in the logging case they studied, and use the few tips they explain, where aspect overhead is around 22%.
CLR Generics implementation
Not read yet, since I'm not playing with that stuff these days, but in the same spirit as the previous article: try to understand what you use, in order to avoid Joel's law of leaky abstraction :-)