I haven't been following the SEMI book-to-bill ratio closely, mostly because I've been doing so much work in the solar space. It's been struggling along below 1.0 for more than a year, though, and really started to slide last July.
That, more than anything explains why semiconductor equipment suppliers are so interested in photovoltaics. Solar is growing fast. ICs are not.
Now, as I've said before I'm not convinced that solar cells are the long-term savior some people claim. But for the short term 50% growth is 50% growth.