Best practices in developing ASP.NET applications

I agree with Chris...
 

string.IsNullOrEmpty:   312 ms
Length:                 140 ms  [fastest]

 
This is not a fair comparison.
 
Need to compare:

(string != null && string.Length !=0)

with:

String.IsNullOrEmpty(string)

Even if the first construct is faster, there is a readability factor:
 

if (!String.IsNullOrEmpty(someString)) {
//do something with someString
...
}

or:

if (someString != null && someString.Length != 0) {
//do something with someString
...
}

The second construct becomes increasingly ugly if there is more than one string to deal with.