Celebrated her 11th birthday last month...
My beloved pristine G4 Cube and its faithful partner in crime, the acrylic 20" ACD. Stock 450 MHz, modded only with the vital goodies - namely, GeForce FX video card, silent SSD and some Spirica heatsinks.
With LeopardAssist, it runs that OS almost as smooth as its younger sibling, an equally pristine - once I get replacement hinges - and capable 1.5GHz G4 PowerBook, which is a mere whippersnapper at only 8 years old.
Of course, I tote an MBA these days for most things work and play, but my love and regular domestic use of these gorgeous PPC machines remains undiminished by time. The un-boxing experience back then was something else too, the little extras, the packaging, the reveal etc. Alas no more given Apple's more recent perfunctory "a charger and be thankful" approach.
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My upgraded G4 Cube 1.2 GHz running Tiger, 12 years old and better then new.
Arggh, you beat me there by mere minutes...still, saved me the trouble of adding a photo aside from my larger ACD
p.s. technically your Cube can't be 12 yet, not until the summer anyway

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Oops, almost forgot I've kindly provided a retirement home - he was going to dispose of it - for my brother's graphite iMac G3 SE DV - also must be at least ten or eleven years young, and in full working order running Tiger with Airport installed.
To my shame, I have to admit this one is currently "employed" as a bedside table

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Mac2 is a 2001 600 SE Flower Power G3 iMac with the max 1GB RAM.
Hippy
Yeah I know it's rare to see one these days, but honestly, I think it's the one colorway that doesn't stand the test of time. Aside from the graphite, I personally really loved the 'sage' green shown in this clever ad...
http://www.youtube.com/watch?v=QkaY-4SfY0g
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