Any product or framework evolves. Mainly it's done to catch up the needs of it's users, leverage new computing powers and simply make it better. Sometimes the primary design goal also changes with the product. C# or .net framework is no exception. As we see, the present day 4th version is very much different comparing with the first one. But thing comes as a barricade to this evolution- backward compatibility.

In most of frameworks/products there are features would have been cut off if there was no need to support backward compatibility. According to you, what are these features in C#/.net?

Please mention one feature per answer.