Electronista summarizes John Gruber's report that a "cone of silence" exists surrounding those developing the tablet and virtually no information comes from those directly involved. Many of the tablet team are reportedly the same as those that developed the Calendar, Mail, and Safari iPhone apps – and those people are used to this. They underwent a similar radio-lockdown in late 2006.
Gruber also maintains that Steve Jobs has given the tablet his "undivided attention" since returning to Apple in September. Apple's secrecy is legendary and Gruber's assertions seem to be more conjecture than insider knowledge. He does admit "I don't know anyone who works at Apple who doubts these things; nor do I know anyone at Apple who knows a whit more. I don't know anyone who's seen the hardware or the software, nor even anyone who knows someone else who has seen the hardware or software."
Gruber does seem more confident that his sources say Mac OS X 10.7 is on track for a developer release at WWDC in June. Unfortunately they haven't mentioned any public-release time frame or a possible name – although I'm hoping for "10.7 Lynx."