I'm not sure if it's been mentioned before in this thread or others, but I would think you need to be careful with the 1.2x book calculations when there is so much cash laying around. Cash is clearly not worth more than 1x book, and with around $42/B share in cash that's not insignificant. If they were to buyback any material number of shares starting at 1.2 book, they would soon be buying above that level.
Imagine for a simplified example that there are exactly 2.5 billion B share equivalents, that the market value is $200/sh, the book value is 166.67/sh (so trading at 1.2/book, which is 416.67 billion total), and they have well over $100B in starting cash. If they did a $100B tender at the $200/sh and it was fully subscribed then 500 million shares would be retired all at 200/sh, leaving 2 billion shares and a new market cap 400B, and a new book value of 316.67B. Assuming the market value is still $200/sh at that point they would now be trading at 1.26 times book.
With that said, I've been a buyer lately in the high 180s and am glad to see it.