Crashes are very rare these days with any machine that is properly configured and running Mac OS X or Windows 2000+ though - the only difference regarding uptime is that some of us will switch our PCs off when not using them, while others will leave them running or put them into standby/hibernate (the latter two counting as uptime as counted by the system).
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Main system: custom C2D 2.66GHz tower/4GB RAM/2600XT 512 MB/500GB HD/XP Pro x86+Vista Business x64
Main Mac: Beige G3 minitower (Sonnet G4 500MHz/640 MB DVD/USB/Radeon 32 MB/OS 9.2.2+10.4.11)