We got news yesterday of a small but important change in Mango, something that we're hardly thrilled about. In short, Mango now has a new security in it's deployment check: Interop Capabilities. While applications approved into the Marketplace (only operator/special applications) and preloaded operator applications can still have this capability, applications with the "IDCAPINTEROPSERVICES" capability listed in the WMAppManifest file will not deploy to the device.

What does this mean? While homebrew applications are still available, no applications using native code can be deployed. That means any COM-based project that uses unofficial APIs (for example, the DllImport project) will be blocked from deployment. All registry editors, file explorers, theme changers, task viewers, etc. All the cool stuff that won't make it into the Marketplace, unfortunately, will no longer be allowed on your own device.

Ouch, Microsoft. 

[Source: WithinWindows]