I'll guess there aren't a great deal of the younger NW Steelie fisherpersons who've ever tied an egg sack. It's been a while since I've even seen the term mentioned in any thread.
With that in mind I just so happened to have fished lots of different bait in a sack and can tell you it is definitely effective in certain systems at certain times. Same can be said of skein eggs, metal and plugs... I like the rest of you never count on just one technique, especially when there are so many to choose from.
For the uninitiated; think woman's stockings cut in patches and those patches filled to the size of a quarter with a favored bait. Example; if I fished the Gualala River in NorCal in the early part of the season I'd likely fill the sack with oil packed tuna, right out of the can... Why? cuz it catches steelhead. Further north, Mad River, Elk, Sixes, etc I may use regular old cocktail shrimp ground up and put in a sack. Then there are those times when juicy cured eggs are best.
Instead of ladies stocking material (it works great) the preferred sack wrapping material may well be a commercial "Atlas Bait Co." product sold at Bi-Mart or any NW tackle shop called "Atlas Spawn Net" and the preferred thread to complete the sack is likely "Atlas Miracle Thread". Rather difficult to explain how one takes the net, thread and bait to make a "Spawn Sack", however if you'd like the instructions visit this site:
http://www.lakemichiganangler.com/tips/salmon_eggs/making_spawn_sacks.htm or Google the words "How to tie spawn sacks", you'll find YouTube videos as well as photo sites.
Some thoughts... since the netting will get caught up in the teeth of your pelagic prey (the fish) it may well be a great idea to tie up some spawn sacks. Since there are preferred baits at different times of the year, why not experiment with Anchovies, Herring, Shrimp, tuna or salmon eggs. Since Pro-Cure is readily available why not soak your made up baits overnight in scents like bloody tuna, anchovies, herring, salmon egg, etc, etc..
Spawn sacks or any baits wrapped in sack material are very versatile.
The first thing to remember; the sack netting material is prone to sticking to or hanging up in the teeth of your prey, giving you a second change to set the hook.
The second benefit is the reality that you can tie up 20 or so baits the night before to have them ready when you are and they are easy to change compared to skein eggs.