What is cool about c# generics, why use them?

I thought I'd offer this softball to whomever would like to hit it out of the park. What are generics, what are the advantages of generics, why, where, how should I use them?

• Allows you to write code/use library methods which are type-safe, i.e. a List<string> is guaranteed to be a list of strings.
• As a result of generics being used the compiler can perform compile-time checks on code for type safety, i.e. are you trying to put an int into that list of strings? Using an ArrayList would cause that to be a less transparent runtime error.
• Faster than using objects as it either avoids boxing/unboxing (where .net has to convert value types to reference types or vice-versa) or casting from objects to the required reference type.
• Allows you to write code which is applicable to many types with the same underlying behaviour, i.e. a Dictionary<string, int> uses the same underlying code as a Dictionary<DateTime, double>; using generics, the framework team only had to write one piece of code to achieve both results with the aforementioned advantages too.