The "once a liar, always a liar" line is a tired and pathetic way to categorically discredit everything Landis says. I find it especially inappropriate to call upon things he said when defending himself against formal charges; like it or not, we can expect just about anybody to deny, deny, deny until the charges against them are conclusively proven.
If anyone really needs a reason why they should at least think about Floyd's recent comments before dismissing them, try considering to what extent these comments (unlike previous denials to doping charges) might fit into the category of 'statements against interest' which the Federal Rules of Evidence consider to be of greater veracity than most statements. Admittedly, Landis may have had many reasons for speaking (as evidenced by the emails), but there's no denying that the context is unique this time.
Another pretty simple reason to listen before judging this time is that (unlike a lot of previous comments) what Floyd is saying this time fits in pretty well with a lot of publicly available information, as many other posters have already observed.
If the goal is simply to catch someone in a lie and permanently discredit that person, then it's certainly easy enough to do the same thing with Lance Armstrong. It would also mean that instead of just lying a lot of the time (and quite amusingly so) that Bill Clinton must have lied about every important thing he ever said. What, bad example?