Yep. Microsoft gave away free software for years (Windows, Visual Studio and Office suites) to students in order to get them excited about their technologies and familiarized with their development environment. One day, those students will graduate and be ready to join the .net (or what-have-you) workforce(). There are entire universities that only offer courses with Microsoft technologies (mine was one such school at one point), so it's not unreasonable or unlikely that Dropbox can infiltrate the education market.

() In some cases, though, Microsoft conditioned students to think that all software should be free... oh, the irony!