I too am thinking of this kind of offer to my dealer. I was set to buy about 3 months ago at full sticker, then something came up and had to put the purchase on hold. Now, I feel like I should be able to get quite a bit off of an e90 M3.
Keep in mind the dealer holdback. I'm pretty sure BMW has a 3% holdback of MSRP. Quick math shows that to be about $1,800 on a $60k M3.