I just cloned angular2-seed project from github and followed the steps, but i got this warning into VS code [ts] Experimental support for decorators is a feature that is subject to change in a future release. Set the 'Exxperimentaldecorators' option to remove this warning.
I had that issue when using @Injectable() on a new service that I created. I had that warning from VS Code's typescript compiler.
The warning disappeared when I added that new service as a provider to the module where I intended to use it.
Hopefully this solves your issue.