It appears that Apple has sent out memo's to all retail Apple store locations letting their employees know that they are putting a blackout/freeze in all vacations for a 3 week window starting with the last week of January.
What is the reasoning for this? Logic and tradition seem to suggest that Apple only does this when a huge product is launched and they need all hands on deck. In addition to the vacation blackout they've kept all holiday season employees on hand to assist.
Our only guess as to what this could be would be the Verizon iPhone launch (or possibly the iPad 2, but that's not likely) - so.... all things being equal this seems to be yet another confirmation that Apple and Verizon have been working on this iPhone together.
More info @ iPhone 4 Forum
(Source: Apple Insider)