I installed Office 2013 customer preview yesterday and all seemed good. Today I needed to create a new document using one of our company standard templates. I opened Word, went to the new document section and was presented with a list of great looking templates, but not my custom ones. The page suggested I used search to find more templates, it did find more templates from the Internet, but did not find my locally stored ones.
Turns out the issue is that the path to my custom templates had been removed as part of the upgrade (from memory in previous versions of Word this path was always default to your local {USER}AppDataroamingmicrosofttemplate you did not usually need to set it).
So I opened the options, added the path to my existing templates folder
Restarted Word and tried to create a new document and this time a got a personal tab on the new document page
When I clicked this I got my list of templates, I really must get round to resaving them with previews so they look better in the list
Update 22 Jan 2014: And if you are looking for the Workgroup templates location as opposed to the personal one they are in now set in Word > File > Options > Advanced > In the General section (near the bottom) press the file locations button.