The $1,800 IRS tax credit for the X5 diesel will be phased out once BMW has sold over 60,000 eligible hybrid and diesel vehicles.
New Energy Tax Credit for Diesels
I wondered when BMW might hit this limit and the tax credit go away, and then I saw this article:
"BMW doesn't typically break out individual model sales but O'Donnell indicated that since the beginning of 2009, over 2,600 diesel 335ds and X5s have been sold."
BMW remains firmly committed to diesel in America — Autoblog Green
Looks like the tax credit should be safe for quite a while.