In this Krzysztof Cwalina post, he mentions the changes to System.Collections in .NET framework 2.0 (yes, 2.0, not 3.0, therefore very prosaic and boring). Of course we know about all that new generics stuff which allows things like List<T>, Collection<T> and Dictionary<TKey,TValue>, which are great things, but further down the list he mentions a new SortedDictionary type:

SortedDictionary<TKey,TValue> does not have a corresponding non-generic collection. It’s similar to SortedList and SortedList<TKey,TValue>, but it’s implemented as a balanced tree (red-black tree). Insertions are on average much faster, but some lookups are slightly slower and memory consumption is larger.

Pretty interesting in light of Luke’s recent aside in the wednesday sessions about the trade-offs of using SortedList versus Hashtable.