New Post: CollectionPropertyAssertions

Yep, you got me right.

By the way, I have asked question at SO about this situation: http://stackoverflow.com/questions/9860026/extension-methods-overload-choice May be this discussion will be useful for you. At least there is a suggestion (in addition to explicity IEnumerable<T> type declaration):

var collection2 = new List<Customer>();
collection2.AsEnumerable().ShouldHave();