When you think too many working hours are on your desk IComerer interface comes to the rescue.
when you use the Array object the interface is used in conjunction with the Array.Sort and Array.BinarySearch methods.
allso if you have an object that is derived from the .Net Collection object. and you need to sort it out then you can count that you are blessed. the .Net Collection has its hands on the matter with the IComperer interface
here is a nice short Example on the usage.
this is an old time saver and probably well known one but there are people that dont know about it and this post is for them.
Got a nice (and short) article that nicely demostrates the usage.