I had a general biology online text. I hated it since the pages loaded so slowly. It may have just been the mastering biology software though but the school's internet is pretty fast so I don't know. I'll just stick to buying used textbooks.
If I really need a text book I can usually find a free PDF of it floating on the Internet. That or go to the library and get what I need really quickly from the reserve book. The amount I use them definitely doesn't warrant any price I've come across.
I purchased maybe ~2-3 physical books for all 4 years...PDF/ebook is the way to go. I usually just had it up on my laptop IF i ever needed to refer to it (which was rare...lecture notes were sufficient for us because they were so detailed).
I loaded it onto my ipad with the expectation that I would just read it...but I never did that, it was always up on my laptop for reference when making note tables and stuff.