What it does say is that the NSA provided the German BND with the technology for its international dragnet search program.
However, that program is not and has never been secret. Its basic functioning is spelled out precisely in §5 through §8 of the G10 Act [1]. This law is hardly uncontroversial, but it is not as though anybody can claim to have been surprised by it; its provisions are well known and frequently and hotly debated.
Regarding information-sharing with the NSA: The law allows the result of §5 surveillance only to be shared with foreign agencies under the conditions of §7a and §8. In particular, this means that all such information sharing has to be reported to the parliamentary commission and the commission has to inform the public about the amount of information sharing that occurred. For 2009-2011 (2011 is the year covered by the most recent report) no such information sharing was reported to have occurred.
Now, if the BND broke that law and shared information with the NSA without telling the parliamentary commission, then this would surprise just about nobody. But that's not what the Spiegel is talking about.
The part that is potentially interesting is the NSA establishing a new "Consolidated Intelligence Center" in Wiesbaden (to replace a similar center in Darmstadt).