I have included a copy of the latest Parallels EULA (as included in the latest updater for Parallels Desktop). The relevant section would appear to be:
"You may use one copy of the Software activated with an activation key on a single personal computer owned, leased, or otherwise controlled by you, at a single time. If you have multiple activation keys for the Software, you may make and use as many copies of the Software as you have activation keys. For purposes of this Agreement, "use" of the Software means loading the Software into the temporary or permanent memory of a computer. Installation of the Software on a network server solely for distribution to other computers is not "use" of the Software, and is permitted, as long as you have an activation key for each computer to which the Software is distributed. The Software may not be used on or distributed to a greater number of computers than you have activation keys. If you use or distribute the Software to multiple users, you must ensure that the number of users does not exceed the number of activation keys you have obtained, or you will be in breach of this Agreement."