Formatting alphanumeric string

You can do it in one line without Linq:

        StringBuilder  splitMe = new StringBuilder("F4194E7CC775F003");
        string joined = splitMe.Insert(12, "-").Insert(8, "-").Insert(4, "-").ToString();

You could do it with a regular expression, though I don't know what the performance of this would be compared to the other methods.

string formattedString = Regex.Replace(yourString, "(\\S{4})\\B", "$1-");

You could put this in an extension method for string too, if you want to do:

yourString.ToDashedFormat();