Nothing equals String.Empty, null does not equal String.Empty, what am I missing here?

In vb6, the default value for a string variable was an empty string. A vb6 programmer relying upon such behavior would be no "worse" than a C programmer relying upon default-zero initialization of int variables; both behaviors were specified as part of the language.

Further, in COM (the framework upon which previous versions of VB6 were based), any time a reference to string was created, someone would have to manually dispose of it. Since the most commonly used string was the empty string, many COM methods are explicitly documented as regarding a null pointer as equivalent to an empty string. This means that a function returning an empty string or passing one as a value parameter or returning one may simply pass a null pointer without having to allocate anything; the recipient of the null pointer will then not have to de-allocate anything.

Because Objects in .net do not require explicit deallocation, the performance advantages of regarding a null reference as an empty string no longer apply. Nonetheless, methods which are called from code that might expect behavior similar to that of COM methods will often regard null string references as being the same as empty strings.

You want

If Not String.IsNullOrEmpty(Request.Params("xxx") Then
    ...
End If

Or

if (!String.IsNullOrEmpty(Request.Params("xxx")) {
    ...
}