I tried to apply @safe/@trusted/@system to Phobos. See also http://lists.puremagic.com/pipermail/phobos/2010-May/000488.html I found this issue there. druntime's modules are not applying @safe/@system/@trusted now. This shows that Exception, TypeInfo, Thread and others are not usable by the @safe function virtually. I hope druntime applies @safe/@trusted/@system.
This is something I'll be working on over the next weeks/months. I have a bit of a monster patch already in-review that needs to be rebased.
*** Issue 5874 has been marked as a duplicate of this issue. ***
This has pretty much been done. If there is anything specific overlooked, please open another issue for it.