- OSX 10.5 on my MBP along with Bootcamp/XP for gaming while away from home (probably the system I use most).
- XP on the gaming monster (Will get Vista for more games in future, and OSX86 because the huge monitor will be great for graphics and video work)
- OSX on my file server (Powermac G4 with RAID card and about 2.5TB of disk space. Will be replaced by a pair of 1TB drives in an external firewire 800 enclosure when I can afford them)
- XP on the P2P system (stripped down all in one motherboard system to keep power usage down). Hasn't been used in months though.
- XP/OSX86 on Gaming PC #2 (OSX is so I can have full access to the file server without fetching the laptop)
- XP on the old PII sat on my workbench (For running MPLAB/PIC programmer and looking up docs while doing electronics stuff)
- OpenBSD on my firewall/router/web server.
- Gentoo Linux (amd64 hardened) on my game server (Dell PowerEdge 1950 that is going to be colocated once I've got all the parts, added more games, and tested it fully)
I'd have to say OpenBSD is my favourite, just because it's so easy to use right from the start, and is made by the most anal programmers out there, so every line of code is close to perfect (has to be to track down security holes).
Gentoo needed a little more poking to get an environment I could work in, and came with a huge problem in that the hardened kernel didn't work with hardened userland until I'd recompiled glibc (only mentioned in one forum thread, and not on the download page/readme).
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You aren't thinking or really existing unless you're willing to risk even your own sanity in the judgment of your existence.