I am an academic biomedical scientist working with electrophysiology. A lot of proprietary software is used in this field, such as IGOR Pro, Matlab, Statistica and SPSS.
These tools are, currently, better than open-source alternatives, and are sadly a little too entrenched in the field.
In terms of statistics software, R is good alternative to SPSS and Statistica, and I tend to use R. GNU Octave is designed to replicate Matlab, and be compatible with Matlab, but it isn't as feature-rich as Matlab yet. IGOR Pro is the most important piece of software in my work, and is used for data acquisition and analysis. Unfortunately, I don't know of any open-source alternatives to IGOR Pro.
Open-source software is crucial to good science, because expensive, proprietary software presents another barrier to replicating experiments and results. Ideally, there should be as few barriers to experimentation as possible. The current proprietary-based system ensures that science is bound to institutions (universities and companies, usually). It is very hard for scientists to work independent of these structures.