Undocumented Linq! .NET 3.5 SP1 Gold Forgot to mention you might break

Undocumented Linq! .NET 3.5 SP1 Gold Forgot to Mention these Critical Changes that might Break your Code BREAKING CHANGE: Cast<T> Behavior Also, a new implementation recognizes queries that apply Where and/or Select to arrays or List<T> and fold pipelines of multiple enumerable objects into single specialized enumerables. According to Dinesh Kulkari at Microsoft this enhancement: "….produces substantial improvement in base overhead of common LINQ to Objects queries (at times 30+%)."