Actually, you can't use IsWhiteSpace to determine which caracter is  
trimmed or not as there are whitespace characters that are not trimmed.  
Furthermore, there are characters that are trimmed but still not listed in  
the documentation.

In the end, to get the proper list you may need to try to trim every  
single character to determine if it will be trimmed with String.Trim()

The code below will display which characters are considered whitespace and  
which will be trimmed.

            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < 65535; i++)
            {
                char c = (char)i;
                string s = c.ToString();

                if (char.IsWhiteSpace(c) || s.Trim().Length == 0)
                {
                    sb.Append(i.ToString("X").PadLeft(4, '0'));
                    if (char.IsWhiteSpace(c))
                        sb.Append("\tWhiteSpace");
                    else
                        sb.Append("\t\t");
                    if (s.Trim().Length == 0)
                        sb.Append("\tTrimmed");
                    sb.AppendLine(); // use sb.Append("\r\n"); for .Net 1.1
                }
            }
            MessageBox.Show(sb.ToString());

Compared to the documentatet list this indicates that U+0085, U+1680,  
U+2028, U+2029 will also be trimmed, despite not being listed, while  
whitespace characters U+180E, U+202F, U+205F will not be trimmed.  
Characters U+200B and U+FEFF is not considered whitespace characters but  
will be trimmed anyway.

Upon even further research, in .Net 1.1 the list is correct and only  
documented characters will be trimmed, but the documentations have not  
been updated for .Net 2.0