FleaFlicker -
I have caught coho with a floating line with skated muddlers or a spider just under the surface. However I really dislike fishing weighted flies (don't fish them for sea-runs, steelhead, salmon or Dollies) so when I want to get deeper (the norm for coho) the sinking line beomes my best option.

That said I know that the "jiggy" action a weighted fly fished on a dry line appeals to coho. However if I'm competing with gear guys for the biters the spider on a sinking line allows me to provide a presentation the coho don't normally see.

Tight lines
Curt