The only reason our Quantum Mechanics prof used TopHat instead was because it gave him the opportunity to gouge an extra $100 out of us for a terrible "textbook" that in any other class would be considered lecture notes, full of errors and typos, proof-read by nobody and held to no standard, with atrocious equation rendering and a terrible interface.
He ended up uploading our assignments to TopHat as PDFs but since it doesn't support PDF-viewing we just download those as zip files anyway. Our in-house service supports PDF-viewing in browser, along with powerpoint and other formats.
Not really sure why TopHat exists besides a way to gouge more money out of us students if we want to be enrolled in a course. I could get by without my professor's poor excuse for a textbook, but I would lose 5% immediately if I couldn't participate in the silly attendance system, and more for the online quizzes (although we could use our in-house system to the same effect) so I have no choice but to fork the money over straight to my professor's pocket. As if my 15k tuition wasn't already enough.
