Non-free math (math that does not meet the terms of the definition given on the page What is Free Math) is not as useful as math that does (see Why Free Math).
But there are other problems with it as well.
It is true that these things are often non-free, and we often don't have good free alternatives!
That is precisely the reason why non-free math should be avoided.
I am not (at this point) suggesting that people should stop reading books, or stop going to lectures. I do suggest that you stop using Mathematica and other non-free software in its class, because we do have free software alternatives already, thanks in a large part to the GNU project.
I would strongly suggest that you not develop further non-free books, lectures, or software. I would also suggest that when you have a free option, to use it – and help and improve it.
Supporting free math is taking a stance in favor of freedom. Supporting non-free math is taking a stance in favor of non-freedom. Using non-free resources (books, lectures…) at this point does not necessarily mean you support non-freedom. But you should only create free math, and when you use a non-free resource you should think about how you can most effectively work to replace it with a free resource!
If you know people who are creating non-free math, encourage them to rethink what they are doing. Have them read the Why Free Math page. Help update that page yourself.
And spend some time working with us on the PlanetMath, HDM, and related projects, to help make more knowledge free in the sense of freedom.
See software we use and software we think is cool for some free mathematics software.
See merits and demerits of non-free webservices for a discussion about why (OK, and also whether) webservices should be free.