We haven't decided yet, but it's likely that if we offer a PDF, it's be
deeply discounted for folks who also buy the book. With the existing
(considerably smaller) books, the PDF is $20, the paper $29.95, but the
two together are $37.50. The prices won't be the same for the PickAxe,
but the concept might be.
I hope you do this, I would like to have the print copy for home and the PDF available for using at work / laptop. As long as the shipping rates to the UK aren't to crippling.
Also, just to add to what some others have said, it was the free copy of Pickaxe that led me to get the paper version. Being able to use it and evaluate it properly was much more useful than gazing at it at the bookshop.
Rob