I've used Mathematica since version 2.2, though I became much more serious with it around version 5. I use it mostly in finance, spanning the exploration of developments in the macro economy, securities valuation, trading strategy development, manager performance analysis, and report generation.
You'll find several demonstrations from me at the Demonstrations Project, including a GIS-based New York subway station locator and a few exploring the characteristics of residential mortgage payments. I have also created freely available conduits for moving financial data from Bloomberg to Mathematica via WSTP. The binaries and source code are available on my GitHub page.