The Vic Farmer is a very good tool for hiking, but when I say multi-tool, I'm really saying multi-pliers. It is debatable whether you really need pliers in the woods, but there are a few other tools that would be handy. I think multi-pliers really come into their own if you are using anything mechanical-- mountain bike, ATV, boat, etc.
I would like to see a multi-tool under 6 ounces with:
Pliers
Scissors
Knife blade
Saw
File
Awl
#2 Phillips
Flat blade screwdriver
Can opener
Removable firesteel
Lanyard mount
The Wenger Handyman has a good selection of features for a knife-based tool and is just 3oz.
You should check out the SOG Paratool. Most of the tools are replaceable. I built a similar set up to what you are describing and the weight came in at 5.9 oz. Must replacement parts were $6 ea from SOG. i.e. It comes with a plain and serrated blade. I dumped the serrated and added a saw. You may be able to replace the bottle opener with scissors by rearranging the default layout.
