I managed to source a copy of Snow Leopard and upgraded my MacBook Air. I am always on the wild and reckless side and shoved in the DVD and upgraded without a recent backup – something I would not attempt with Windows.
The upgrade process takes about 60 minutes and after reboot all applications still work (one exception was an outdated 3G driver which I installed once, but never used). Unlike with Windows 7, where the UI is completely revamped, you will struggle to find something new in 10.6 (most obvious is the wireless drop-down, a revamped Quicktime Player and the seamless inclusion of Exchange support).
The OS boots up / shuts down faster and feels generally slightly faster. The Exchange support works well (bye bye Entourage) and Apple managed not to break anything. Awesome release – especially considering it only costs R 325,00.