On January 28th, in fact. You'll finally be able to go mock the people you're stomping in WvW (or deride the people stomping you, natch). There are a few caveats, however:

• BE SURE TO MOVE YOUR ACCOUNT TO YOUR DESIRED HOME SERVER BY THE 28TH! That's the deadline for the current, free transfers.
• Players who have a North American home server will not be able to guest on European servers, and vice-versa. This is due to regional data center restrictions.
• Guesting players may not participate in World vs. World. Entering WvW from anywhere besides your home server will transfer you back to that home server.
• A player may have only two active guesting servers at a time. After 24 hours, the slot you've reserved for a particular server will open, allowing you to choose another. During those 24 hours, a guest server will not limit your access.
• You may still find yourself on an overflow server if you guest somewhere with a high population.
• When guesting is implemented, regular server transfers will no longer be free. The gem fee for transferring will be dependent on the population of the server you move to (i.e. low-pop servers will be less expensive). In addition, transfers will be limited to one per week and you may not move your account to a server that is designated "Full."

I'd be remiss in my slimy peddling if I didn't take this opportunity to mention Lincoln Force, the Giant Bomb community guild, and how you should transfer to Yak's Bend while the going is still free to join us in our antics. All the cool kids are doing it.