Most Tiger books are showing a publish date of either 3/24 or 3/25.
I use to be excited about that little "find," but I suspect it is just a generic publishing date and could easily change.
Given the recent rumors of new found functionality in the Tiger builds, including the fact that Steve was using a build at MWSF that is more current than what developers have seen, I suspect Apple is still in development mode, and will start a true beta some time in February.
My bet nowadays is we will see Tiger released at WWDC. Apple can demo to the press and developers new functionality not show publicly, and get developers fired up to build apps for Tiger.
Given this is the last OS upgrade for a couple of years, I am happy to have Apple put as much into Tiger as possible. I'll gladly wait until June for a markedly better OS with tons of new features, less bugs, and more security due diligence.