The Mercedes E320 CDI is expected to pass the more stringent EPA emissions regs soon:

http://www.aceee.org/transportation/taxcredits06.pdf

Buyers will recieve a $1300 tax credit for the purchase while receiving an adjusted city mileage of 31mpg.

This is all very good news for hopeful diesel Jeep buyers in the US because this is supposedly the same engine that will be in the Grand Cherokee as an option beginning in 2007.
While the $1300 credit may not seem like much, one must remember the EPA/IRS languange will most likely give the GC a higher tax credit based upon it's larger SUV footprint/wheelbase.

Again I say, if you are interested in a diesel Wrangler for the US make your thoughts known to the manufacturer either through the DR.Z campaign or:

http://www.jeep.com/wccsapp/universal/J/index.jsp?appStr=wccs&titleStr=Contact+Jeep&familyStr=brand&franchise=J&actionURL=%2Fwccs%2Fbrand_forms%2Fus%2Fwebform.jsp&promotion=null&category=N