If it works like my Saab and VW do, they needed to program the car for both keys at the same time for you. It's probably one of those "of course" things, but thought I'd mention it just in case.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)