Cornerback is an instincts and tools position. Miller has the tools but not the instincts for it at this point. So much of a corner's job depends on being right where you need to be at a specific moment. His poor technique on tackling can be corrected, but that will only improve things if he develops the instincts to break on the ball or give it up and take the man. Right now he's a pretty weak target on the field. David Barrett has much weaker tools than Miller but he has excellent instincts and it shows up in a lot of passes defended down the field and very few pass interference calls.
Look for one big signing and many smaller solid signings, its going to be the blueprint around here for quite some time. I agree Sandman, you really do not know what kind of shape you are in until you re-sign everyone you would like to. The Jets are better in this respect than many other teams, but it will not make up the difference between team like us and Buffalo or Arizona who are also pretty solid with their roster contracts.
