Are you seeing any disk latency?
I don't think so, although our LUN's are starting to get a little crowded with a number of VM's on them, 25-30 vmdk's per. We have another tray we're about to add to our FC san next week.
I would confirm disk is responding as it should. Latency has a bigger effect on environments with lots of small files (like a profile).
What type of storage and configuration?
Update - I might have jumped the gun on the storage investigation.
Take a look at this post http://blogs.technet.com/b/markrussinovich/archive/2010/12/07/3373406.aspx
Special considerations for AppData\Roaming folder:
If the AppData folder is redirected, some applications may experience performance issues because they will be accessing this folder over the network. If that is the case, it is recommended that you configure the following Group Policy setting to sync the AppData\Roaming folder only at logon and logoff and use the local cache while the user is logged on. While this may have an impact on logon/logoff speeds, the user experience may be better since applications will not freeze due to network latency.
User configuration>Administrative Templates>System>User Profiles>Network directories to sync at Logon/Logoff.
If applications continue to experience issues, you should consider excluding AppData from Folder Redirection – the downside of doing so is that it may increase your logon/logoff time.