I was just playing around with the Complete Baseball Encyclopedia, looking for a “comp” on Johan Santana – based on his throwing hand, age, innings thrown, and effectiveness (in terms of ERA against the league and RSAA). And, this is what I found:

Hey, we know that Ford guy, right?
Does this mean that Johan Santana has another very good seven years in him, like Whitey Ford did? Of course not – it only shows you how Johan has performed, to date. And, he’s been Whitey Ford-like.
But, in fact, we know that, two years ago, Barry Zito looked like a good Whitey Ford comp too – and, we know how Zito is doing now.
You know, the Red Sox have been very good at this “trade for a starter and lock him up” thing. See Pedro Martinez, Curt Schilling and Josh Beckett. The Yankees? Well, they’re not so good at it (under Brian Cashman). See Javier Vazquez, Randy Johnson and Jeff Weaver.
If the Yankees are going to make a big play for Johan Santana, I hope they really know what to look for, now, and have learned from their mistakes in the past.
To me, the key is “Age, Injury-potential, and Make-up.”
Checking Johan’s age is simple – and, he passes the test there. As far as the soundness of his body, one would hope that the Yankees would check out his shoulder, elbow, forearm, etc., with great detail before signing him to a long deal.
The attitude thing is the tough nut. Does he have that borderline-cockiness confidence when he’s on the mound? Basically, is he a win-day pitcher – meaning the day he pitches, you win (because he’s someone who finds getting beat to be unacceptable)? Can he handle October? Is he the guy who wants the ball in Games 1, 4, and 7 of a seven-game series? Can he handle New York? Is he smart enough to play nice with the media or strong enough to block them out and not care what they say?
I don’t know the answers to these questions. And, I’m not sure how the Yankees will find these answers – but, they better…before they pull the trigger on a deal for Santana.