I am running the RTM / Enterprise Evaluation (Build 9200) of Win8 and VirtualBox 4.2.4 r81684 on Mac OS 10.8 and am finding the experience a solid one so far. I do not have a Windows 7 system to upgrade, so my installation is extremely clean and the only bump I ran into was needing to run the Guest Addition (drivers) for Win8 by hand following the manual installation instructions.
The installation process has succeeded 4 times in a row as I experiment with different settings for the VM and display - so I would say you might dive in once you've made a backup of your existing Windows 7 setup and have time to upgrade. I know almost nothing about Windows these days and haven't needed too much research or assistance in getting things set up.
The guest additions actually fixed a display issue I had where full screen wasn't with the generic drivers that Windows installed. The guest additions made the OS much more usable for me.