The Team Fortress 2 Blog has an update from Valve designer Greg Cherlin following up on the patch released earlier this week that included balance changes for Team Fortress 2 (thanks JaZeeL). The update includes a primer on how the new critical hit system operates under the hood and their reasons for changing how critical hits work. He offers statistics on the system and the changes, and a chart illustrating the old system versus the new one. He summarizes the situation by outlining the strategic implications of the system:

In thinking about the change we wanted to make to critical hits, we decided that there was a point on the graph of particular interest to us, and that was the point at which your critical hit chance was as much a result of your performance as it was the base chance. If you look at at (A) on the old line, you'll see that point isn't reached until you've done 550 recent damage, a feat that occurs about as often as our backstab code works correctly. That point is reached at (B) on the new line, around the point where you've done 175 recent damage. This means that if you've just singlehandedly killed an enemy Demoman/Soldier/Pyro/Heavy, your next 20 seconds worth of crit chances are already more a result of that kill than the base chance. As a result, if you're a highly skilled player, you're going to fire significantly more critical hits than those around you. And remember, if you've just killed 2 or 3 enemies, now's the time to push!