Turk,
Sight in your rifle 3 inches high at 100 yards. If you are shooting any "standard cartridge" (ie .270, .30-06, 7mm mag) it will be about 4 inches high at 200 yards, and pretty much around zero at 300. What this does is allow you to sight in on the about 8 to 12 inch vital zone of an elk, and not have to worry about bullet drop out to around 350 yards. Remember that this is bench type shooting.
I've got a Bushnell rangefinder, and I use it like CR Sam said - scouting I make a call how far the critter is - then verify with rangefinder. I used it Saturday to after setting up some paper plate targets down in and across a draw, and then shooting (offhand, sitting and prone) to check distances after shots (results mixed - mostly good).
As to actually using the range finder during elk hunting - well I don't. Two reasons. If you are sitting at the edge of a meadow, yes you can use the range finder to figure out how far it is to some feature that an elk beast might walk out by - but if you sighted in like above you can pretty much figure if that is within 300 yards or so without the finder. So you are just verifying what you already know. Second reason is the much more common situation. You see the elk, and things begin to happen real fast. You may have to move to get a clear shot or the elk is already moving, or both. Shot over a hundred yards? You better get in some sort of braced shooting position. You're at 10,000 feet - air is thin - you are out of breath. Now exactly when do you use the rangefinder? The elk ain't gonna hang around till you get set up. This is not bench shooting - you have to make a good shot on that 8 to 12 inch area - right now!
Bottom line - spend the money on a good set of binoculars. If you can see the elk without it seeing you, you can stalk in to a good shot. Binoculars are essential to western hunting, range finder is a nice to have.
JohnDog - Is it October 19 th yet?