I always had trouble telling if a steak is done by touch. I know there is some finger test rule of thumb using your thumb touching different fingers, then touching the fleshy area under your thumb, then touching the steak Maybe I am just not a touchy-feely sort of guy, but it has never worked for me.
I find the instant read thermometer works better, with 130135° being my target medium-rare Steak (140145° for medium). The only problem is I dont like poking the steak every couple of minutes to find out if it is done. I am afraid I am releasing all the juices.
Now there is a steak timer app that figures when your steak is done for you! Omaha Steaks has a free iPhone app with a steak timer. Just set how thick the steak is and how you like it cooked (rare, medium, etc.). The app sets a timer that tells you when to flip your steak and when to take it off the grill. It also can run multiple timers at the same time. You can check your steak with an instant read thermometer after you pull it off the grill just to make sure it is done, but that is a lot better than poking it a bunch of times. The timer is for a hot grill (the high setting on a gas grill) and can be adjusted if you have a cooler or hotter grill than the default time it is set on. Once you get it zeroed in you can pretty much skip the instant read thermometer all together.
Don't have an iPhone? Omaha Steaks also has a steaks cooking time chart on their web site.