It's designed for educators, not students, so there are frequent gaps in the individual courses (in one I couldn't even figure out how it might be useful to an educator trying to use it for the basis of a class).
A number are crippled by copyright, or, rather, you'll need access to a research library to get copies of all the papers in the required reading list.
And there are gaps in which courses have been captured. E.g. first term inorganic chemistry is missing and OCW has no plans as of a year or so ago to address this.
There's also the not so minor detail of science laboratories. With a lot of work you could probably make do for physics but chemistry and biology would be right out; you'd probably need to find a college that would be willing to let you take just those labs, although at least in the case of chemistry they often aren't separate classes.
A lot of course require Matlab, which the last time I checked would require a non-student to pay around $1,800 for a copy.
All that said, a really disciplined autodidact can get a good education with the many resources on the web.
Mind you, it ain't like doing it via distance learning is cheap either - I think Kaplan/Concord charge about $10k a year, and distance learning requires 4 years rather than 3. On the other hand, the nearest ABA school to me (UC Hastings in SF) runs about $35k a year in tuition fees. It's become a very remunerative field; apparently the average law school professor earns about 20% more than a supreme Court Justice.
I.e. "If something can't go on forever it won't", and higher education inflation is certainly an example of that. Here's the Instapundit (a law professor) on this: "A recent Money magazine report notes: 'After adjusting for financial aid, the amount families pay for college has skyrocketed 439 percent since 1982.'" (http://www.washingtonexaminer.com/opinion/columns/Sunday_Ref...).
And as one article noted, The next generation of home buyers has too much college debt: http://bayarearealestatetrends.com/2010/06/the-next-generati...
College debt is of course non-dischargeable (can't escape it through bankruptcy), so when you combine all the above with the drastically reduced returns due to the Great Recession, including the ugly fact that history shows that people entering the work force during bad economic times have sharply reduced lifetime earnings....
See also, Lesson 6 of Gian-Carlo Rota's "Ten Lessons": http://www.math.tamu.edu/~cyan/Rota/mitless.html
"You must measure up to a very high level of performance. I can imagine a propective student or parent asking, "Why should I (or my child) take calculus at MIT rather than at Oshkosh College? Isn't the material practically identical, no matter where it is taught, while the cost varies a great deal?"
One answer to this question would be following: One learns a lot more when taking calculus from someone who is doing research in mathematical analysis than from someone who has never published a word on the subject. But this is not the answer; some teachers who have never done any research are much better at conveying the ideas of calculus than the most brilliant mathematicians.
What matters most is the ambiance in which the course is taught; a gifted student will thrive in the company of other gifted students. An MIT undergraduate will be challenged by the level of proficiency that is expected of everyone at MIT, students and faculty. The expectation of high standards is unconsciously absorbed and adopted by the students, and they carry it with them for life."
That said, one must weight these benefits against the cost of attendance.
In general they simply provide better opportunities:
- networking
- brand recognition of institution
- head hunters that look for talent pre-graduation
That said, I think you can get an excellent education with online and offline materials (don't discount the latter... a good book and some solid study hours every day will still get you pretty far). You'll just be at a disadvantage on the above points. It's possible to route around those limitations however.
