I tested 1.6.2-1.7.4
video:
http://youtu.be/p8IJ2yWaApo

(video 0:33)
The redstone directly point to the piston/hopper/TNT (transparent redstone type block, so it cannot block redstone on the edge). But they won't get power.

(video 0:43)
need another redstone next to the original redstone to power the block.

(video 1:07)
or another redstone below 1 block, but transparent block connot transfer redstone signal downward. so that redstone should not affect the whole system, but it did.

(video 1:53)
same as hopper

(video 4:18)
same as TNT