Thanks for all the feedback everyone. It is much appreciated. I am definately leaning towards charging for a PDF and am giving serious consideration to the Lulu book option.
My intention is not to make money from the instruction guide. I have an active art practice, a busy commercial studio and a photography school that combine to keep milk in the fridge as it were. I simply wish to recoup some of the costs of the project. More importantly, especially if I go with something like Lulu, I will be able to offer a quick and easy service of either a download or a book to anyone who wants one without having to personally field calls, emails etc. and deal with shipping. All in all, it seems like a win-win situation.
My only concern at this point is the quality of Lulu's printing service. I have never seen a Lulu book (that I know of) but I have seen iBooks from Apple. I was quite impressed by the quality of those. So, what is the print quality like from Lulu? And has anyone ever used them for their own project? (or should I do a search of the archives...this may have been discussed before...sorry if it has...).
Anyway, I'm rambling. Cheerio and thanks again for the advice.