If you are evaluating Windows 8.1 in an enterprise environment that also contains logon scripts there is a new Group Policy setting you should be aware of. Windows 8.1 by default delays logon scripts for 5 minutes. There are many poorly written or misbehaving logon scripts out there, the 5 minute delay will ensure that the user's desktop remains responsive during the logon process. However, this may come as a surprise for many organizations especially since the intent of most logon scripts is to perform some action prior to the user interacting with the desktop.
Group Policy preferences have pretty much eliminated most of what logon scripts used to do and I recommend verifying that what the logon script is meant to accomplish cannot be done using Group Policy prior to writing a logon script; however, in case your organization does still need logon scripts without the delay and plans on deploying Windows 8.1, you may want to change the following Group Policy setting to ensure that the logon script runs as expected:
Computer Configuration > Administrative Templates > System > Group Policy > Configure Logon Script Delay