Many people I know (that work in restaurants serving steak) use the hand method of testing doneness:
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Using the palm of your hand, follow the instructions below. This is how meat will feel to the touch when it has reached the indicated doneness.

Rare: Squeeze the pad at the base of your thumb. It should feel spongy and offer very little resistance.

Medium: Press on the middle of the palm of your outstretched hand. It should feel firm and snap back quickly.

Well-Done: Squeeze the base of your small finger. It should feel very firm with almost no give. (For best flavor it is not recommended that you cook your steak to well-done.)
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Personally I just make an incision and look at it. So if you don't like anyone making the first cut into your steak, don't have me make it. Meat thermometers don't work worth jack in things like steaks, I find.

When it doubt, check it out.

Also, steakhouses seem to undercook steaks by 1 or 2 levels... and there's usually a level or so difference in people's judgements...

Mine are:
Well - solid colour throughout, no free running juices
Medium well - inside is slightly pink, juices mostly colourless
Medium - inside is pink, juices run pink to red
Medium Rare - inside is pink to red, juices run red
Rare - inside is red, blood everywhere
Blue Rare - I wave an acetylene torch near your steak, enjoy your tapeworm



Bren R.