I mostly use OpenSuse.
But have installed, and "managed":
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OpenSuse: My workhorse.
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Slackware. My very first linux experience. Still have an Slackware PC somewhere on my Mom's home (for her to use)
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Ubuntu. I have help some family members to maintain an Ubuntu linux System on their laptops. Maybe 2 or 3.
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CentOs. At work
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Linux Puppy (On an USB drive), when I want to leave No trace.
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Fedora. Installed this a couple of times. It took longer to install that to de-install (sorry
)
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Gentoo. I love that damn thing. But it superseeds my interest with "hardware contact". It's just way toooooo geeky. I installed it once, and I was loving it, until I miserably failed to get the X-Window system with KDE4 going. After 1 week of a fight, it was time to drop back to good old Suse.