I have been using computers with Linux and with some UNIXes 20 years. From about 2002 I have an UNIX workstation at home.
As you may guess, I never used the UNIX workstations for their performance. There have been different reasons: the stability, ther reliability and the style.
My first non-work UNIX machine was the SGI Indy - an iconic desktop machine. Mine was a very low end one with 32 MB of RAM and a limiteds R4600/133PC processor. I had to expand it to R4400/175 processor adn 128 MB of RAM (later to the full 256 MB). Then it was a quite powerfull box: I developed some nice FEA codes on this machine and also typeset several logner texts in the LaTeX (not mention the normal desktop tasks like image editing, drawing, scanning, music playback and more). I stil have this box as a secondary device.
My Indy has an XL graphics board which features some OpenGL 1.1 acceleration. So I also played with OpenGL codes quite a lot.
Of course that machine was in 2002 (and still is, of course) too slow for larger computations. But a C code development (Vim + gcc + Links and manual pages for documentation) with simultageous music playback (no matter if mp3/ogg or from Audio CD) was a normal routine.
The sound and music is an another story: the Indy has a great audio subsystem and even it's integrated mono speaker is enough for a "normal" music playback. The external Toshiba SCSI CD-ROM allows a very low CPU use for music. The sofwtware-only MP3 or OGG playback means higher CPU use but is's still under 5%.
The Indy is also very quiet - it starts the PSU fan (its only fan) only is rare occasions. The main (and mostly the only) noise comes from the SCSI disk.
I got an O2 in 2005. It's noticeably faster than the Indy but it is also more noisy. Many other good features remain. The plastics feels more fragile, the sound from integrated speaker is not that nice (but it's still acceptable) but there is and integrated CD drive (can be even a CD=RW or a DVD) and the O2 accepts wider range of monitors.
I upgraded my box to 1 GB of RAM and replaced the 8 GB disk with a 36 GB one. And that are almost all upgrades. Of course the CPU power was enough in 2005 but the situation is much worse in 2015. Especially the WWW browsers are problem (the situation with the Mozilla/Firefox was always bad - they are traditionally slow on most of SGIs for many reasons). But the power is still enough for many tasks so I see no reasons to replace the computer.
Why I still use the box? Well, I don't know. I feel the best with it (I do use Ubuntu and Windows computers at work but I don't like them). The things work in way that I expect, the OS (and the machine) is stable and it's behaviour is predictable for me. And the software is not changing so there are no new unexpected features (or loses and changes of functions).
For example, on a Linux machines I have used during the time these desktop
environements: the WindowMaker, the FVWM, the KDE (1.x, 2.x) and the
GNOME (1.x, 2.x and 3.x for a short time), then different versions
of the Unity (both 3D and 2D) - most of them were preinstalled by
default in certain versions of Linux distributions (as you may
remember the Ubuntu used GNOME and then switched to the Unity, for
On my SGIs I use FVWM (on the O2) and 4Dwm (the default desktop) on the Indy (OK, I had the FVWM here for some time, too) witout chnages for more than 10 years.
During the time I also had a SGI Indigo2 (too purple, too big, a bit noisy but an extremely responsible) and a SGI Fuel (it was fast but far too noisy for me).
I had (or still have) some machines from other vendors: some HPs (never used them for an actual work), some IBM Power boxes and some Suns (the Blade 100 at the moment but my most actively used Sun was an Ultra 10). For some irrational reasons I prefer the SGI machines (maybe I do hate the CDE desktop?). I don't count Apple's OS X equipped machines as an UNIX boxes (though technically they are UNIX workstations). Anyway, I used some Apples in the past (the white iBook G3 was my only notebook for a few years) but now I use my iMac G5 very rarely.
P.S. There is near nothing about the software - to be continued later...