I also started on X11 at RPI around 1987, first in the CS Dept Sun Lab and later the PAWL. The CS Dept had some cool stuff back then -- Sequent Balance 21000 16-node shared-memory machine, Intel 32-node hypercube with message-passing, an SGI workstation, and the CAM-6 (Cellular Automata Machine). And their main workhorse VAX running some flavor of BSD if I remember correctly. They also had some other machine running AT&T System V, but I didn't like it as much because of the differences from BSD.
I wrote some low-level X11 code to display raster images very quickly for lattice animation, and still use the code to this day (for a while I used it under Linux, now I use it under Mac OS-X). It's so low-level, the first version I wrote for 1-bit displays depended on the order of bits within bytes and bytes within words, and when I ran it on a DEC workstation one time I found that that architecture had things packed together in the opposite order, and I needed to tweak the code to make it work there. Later I eventually updated the code to use 8-bit colormaps. I got pretty spoiled, being able to write some code and then still use it 20+ years later.