I have a 2010 Mac Pro running 10.6.8 and I have not upgraded to Mavericks. Everything that I run with this computer works just fine, both hardware (NEC monitor, Epson 3880, Nikon Coolscan scanner, etc.) and software (PS CS6, NEC Spectraview II, Topaz & NIK plugins, PT Gui, MS Office, etc.). So why change the operating system if everything works fine as it is. I know that if I upgraded, it would turn into a headache for sure.
Personally I'm tired of this treadmill of constant upgrades and drain on my pocket book (yes, I know Mavericks is free), so I'm "freezing" my entire system (computers, cameras, and software) for the next 3 - 4 years and instead of fighting with equipment and learning new software I'm going to spend my time doing what I enjoy most, which is taking pictures.