I love Skybonus. Delta not only gives GM+ double Skymiles, but if you have a business and a Skybonus account you are getting even more than that. Tell me another airline that rewards business as much as Delta! I have blogged about Skybonus before HERE and you can read all about it.
So take a look at the current bonus that is going on till the end of this year. You can download a PDF of the promotion HERE for the full T&C. The bottom line is you need to sign up for a new Skybonus account by using this link HERE. Then, you will need to fly within 60 days of enrollment with the code!
While the Skybonus points are not as valuable as Skymiles I tend to use mine for Skyclub passes (takes 30k) or for 10 pack of amenity / drink coupons (takes just 10k). Enjoy – Rene