From what I have gleaned though some adverts and post in various Irish forums a lot of e63 650i when new were "accidentally" registered as 3.0L cars not as 4.4L cars. $400 a year savings in tax so yes, it has been taken advantage of...
Here's an example of one such car:
http://www.bmw-driver.net/forum/showthread.php?t=59473
(e63 650i being referred to here also in post #50;' http://www.boards.ie/vbulletin/showt...7395210&page=4)