Why is Dictionary preferred over Hashtable in C#?

Question

In most programming languages, dictionaries are preferred over hashtables. What are the reasons behind that?

Answer 1

Since .NET Framework 3.5 there is also a HashSet which provides all the pros of the Dictionary if you need only the keys and no values.

So if you use a Dictionary and always set the value to null to simulate the type safe hash table you should maybe consider switching to the HashSet.