Anything that you want in print or as a reference can be printed up without violating the Safari TOS. I have found that many times I'll get a book on Safari and be like "I'm glad I didn't buy it, better delete it from my shelf", or I'll only refer to a couple sections of a book over and over again. Those that I actually use the whole book for (For instance, Mastering Perl/Tk) I actually buy. I've found it's saved me quite a bit of money and increased the average quality of my bookshelf quite a bit.
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