Not a Good Idea, if your suddenly need more taht 2 processors you wil have issues untiol ESX 3.0 is relaesed this year. Oneworld can be processor intensive depending on number of users accessing the platform
Citrix on the other hand - No Issues, Obviously you will need to qualify the packaged apps first to ensure they wouldn't kill the box. a good feature for citrix is the UNDO mode when publishing a New app, you can undo the changes, even installing a SP all changes will 100% be un-done.
There are many great features about VMware.
I'm sold on it!
Dameon