It has been a longstanding (if anything in Windows 8 can be considered longstanding at this point :P ) issue in Windows 8 that local admin users don't retain mapped network drives that are... dictated (lack of a better word) by GP.

more info: Group Policy Preferences Drive Maps Not Working in Windows 8 RTM When "Reconnect" Option is Active

Apparently you could get around this by manually mapping them and un-checking "reconnect at sign-in" but this opens up some other potential problems.

However at work today after a round of updates (released on the 12th).... there were my mapped drives! And I hadn't previously manually mapped them (I just had crappy shortcuts to the folders on my desktop). All 3 of em.

Anyhow, for anyone experiencing this issue, I am tentatively confirming that MS has released a fix for this over Windows Update, although I can't tell you the exact KB that hits it.

In the future, when my IT beard is long and over beers with the newbie in the office, I'll be like "I was there man. The day the drives mapped."

edit: Seems to KB2795944 that does it