Actually it is not completely pointless today: Some months ago I used it to speed up an force-directed algorithm which spent 80% of its time in calculating normalized vectors between two points - and the fast inverse sqrt actually helped to speed up the program by a factor of 2.5 to 3.0. The reason why i used it is quite simple: In (unsafe) .NET code you can execute all the necessary arithmetic operations (pointer casts, bit shifts) but you are not allowed to execute arbitrary x86 operations.