Yep. I own both a Octane 2 and an Indigo 2. For my final year project for my CS degree I wrote a cross platform, multi-threaded voice over IP program for both SGI IRIX and Linux - that was eleven years ago.
All of the machines are extremely well made - the build quality makes even the best PC look like it was assembled by a child in comparison. And of course, the graphics hardware, compared to contemporary equivalents, is very advanced.
At the time IRIX was a very good version of Unix; extremely stable and scaled from a single processor workstation right up to the giant Onyx and Origin systems with dozens and dozens of processors. It still has some features not in modern versions of Linux or OS X, but the interface is now looking quite dated in comparison (for the last 10-15 years of its life the desktop interface didn't really change at all) and it can be a pain to get recent free software to compile (eg a better browser than the built-in Netscape Navigator 4!).
The O2 is a quiet workstation (most SGI systems are noisy!) - though has only a single graphics hardware option in comparison to other systems which usually have several - and has analogue AV input and output built in.
The Indigo2, Octane and Fuel workstations are better general purpose machines than the O2, IMO. Though none of the SGI systems are as flexible as a PC - they're usually targetted at a specific market and don't have as many add-ons or options available (eg no USB in anything other than the very last models - and then only keyboard/mouse support).
My collection database and technical wiki:
https://www.target-earth.net