Right now we're trying to work around the 500 error on the VMs that we use for capturing apps for AppStacks. We had been installing those apps as the local administrator account. My thought was so that the AppStack doesn't contain other user profile folders in them. I am hoping that it does NOT capture the user's profile folder but I will have to test this more and I will post back my findings, unless somebody else knows what the best practice is for creating AppStacks.
Nail -- Hammer -- Head 
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I saw the exact same thing but we already had a few applications that needed to be packaged as a domain account so we just have to make sure to use an account that doesn't have any assignments and we are good to go. And just so you know, Appstacks DO NOT contain any profile information. It doesn't contain any user related settings or files for that matter. All and everything that is created in c:\Users or HKCU is not being stored in the Appstack. For as far as I'm concerned looking at it as a packager this is good news. You get clean application installations. Only downside is that you still have those occasional developing idiots that store the application in the %APPDATA% "because a user has permissions there"..
Regarding the writable volume. Normally the only thing that changes in the writable template is the snapvol.cfg which only holds info on what to store and what not to store in the writable and the version number (which is a txt file ). We did test with my very old 2.6 template (yes, we still have some of those ) and it worked quite well to be honest. svservice however is a different thing. It could be that filter drivers changed and the snapvol.cfg needs to be changed. If this is the case you can still update the writable by using the manager. If so, could you please let us know? Looking at upgrading to 2.12 in a few weeks .