I have taken a handful of courses online and will be starting the Creighton web-based program this fall. In my experience, I think that online courses require a lot more motivation for you to *want* to learn the material. Two of my gen ed online classes (logic and macroeconomics) were very easy with little to no busy work - weekly assignments and that was it. Logic had open book exams, but Econ we had to go to campus for closed-book, proctered tests. My current Psych class is the same way - weekly online, open book quizzes with on-campus, closed book exams.
I did take 2 science courses online too - A&P I and II. Technically these didn't require lab components, but we did have "lab" assignments. We had no exams, but 2 very long homework assignments each week. I found these classes to be just as difficult (if not moreso!) than many of the science courses I took as an undergrad. All of my online courses were through a CC.
Bottom line is that it all depends on your instructor (just like with any campus-based course!). Jack makes a good point about checking with prospective schools regarding their policy - the only restriction I've seen for schools I researched was that they would not accept online science courses, but made no mention of gen ed pre-reqs, and not every school has that restriction. I'm not sure if you are thinking of doing all pre-req coursework online, or just a few pre-reqs, but previous posters' points are well-made in that lab components will most likely have to be done on campus.