I just purchased an F90BT with the 10% electronics coupon PLUS the 30% cashback program. The 30% is in my live account and pending. I guess only time will tell if it comes through but everything seems fine so far.
One thing to note is that they seller receives their 100% and ebay takes the hit on the 10%. However, the live cashback amount is the original 100% amount. They seem so far to be mutually exclusive. It seems that ebay takes the electronics coupon hit and Microsoft gets hit with the 30%.