Parallels running 100% fine on my side on OS X 10.10. I have 2 VM's both tested OK without regression so far : Win XP Pro and Win7 64bits and both VM run fine in all modes (coherence & standalone) with sharing OK. I'll continue to test various features and especiallly interactions with Finder, but so far I'm 100% happy especially I have just moved from vmware fusion who's 100% NOT working with OS X 10.10 ...
Parallels works fine on Yosemite - it's attempting to install Yosemite as a guest OS/VM that is not working at this time. Given that the DP has barely been out for 48 hours, I'm not terribly concerned about it at this time. But other OSes (Chrome, Linux, Windows, Mavericks) still run fine as VMs in Parallels.
Funny I thought you said GI tract On the rest you're totally right. We support roughly 22000 users and a City of 4.5 million so our audience is large too I've already installed on some spare hardware. However the VM route is always best as you can install/revert, reinstall etc and make on the fly changes that hardware is less well suited for. Reinstalling the OS from scratch takes an hour. Cloning the main drive takes 15-20 mins. Resetting the VM takes 30-45 seconds on our machines...when testing dozens of software and installer options and changes for clients you can see why we choose a VM for this. Parallels is still hands down the best VM package for us...memory management is far better with multiple VMs than our tests with VMware. It's just a matter of waiting and pressing for timely updates.