These privileges are more than enough for a member of this group to be able to install a malicious file onto the system so that an administrator of the machine could execute it and completely compromise the system.
This being the case, unless you have a specific reason for a group of users to be members of the power users group then they should probably be in the users group. If you must have them in the power users group then a good idea is to use group policy to further enhance the security of those machines being accessed.
Chris Sanders is the network administrator for one of the largest public school systems in the state of Kentucky. Chris's specialties include general network administration, windows server 2003, wireless networking, and security. You can view Chris' personal website at www.chrissanders.org.