Used a few desktop Sun 3 machines (I think they were 3/60) in the late 80s. Not the GUI, but just remote login, using them as CPU servers for computational simulation. That's because the CS department had a few dozen of them, and they were not using any CPU time, so science groups on campus were allowed to run CPU-intensive jobs on them, to help justify spending all the money. In reality, the CS department had bought them as status symbols: they had a GUI, while everyone else on campus was still using VTxxx or 327x terminals. They were dog slow, in particular their floating point. Made me really appreciate the VAXen and the DECstation. But at least their Fortran compiler was functional, unlike the NeXT machines (which were also dog slow, and their compiler was laughably broken, I gave up on those).
Then helped a fellow graduate student set up a server class machine (3/2xx of some sort) which was a workgroup server. The hardest part was getting the AppleTalk networking to work (to serve existing Macs, of which that group had quite a few). The OS back then was very borken as far as networking was concerned. Or maybe it just wasn't designed to be used in anything other than trivial configurations.
Never used Sun 4 (SPARC) machines; by that time, I had access to much faster hardware (RS/6000, PA-RISC and then Alpha), and the 32-bit SPARC machine were slow by comparison. The funny thing is that later in life, the chief architect of the SPARC ended up being my manager for many years, and is still a friend.