In fact, I have only seen this once.
And I saw it on the first week the game went live.
I realize that we have gone around, here and elsewhere, on the idea that the number of subscribers is not a direct indication of the health or profitibility of an MMO.
On the other hand, with a new game that is getting good reviews and that has a strong IP behind it, I would expect to see this message more and more as time went along, eventually leading to the addition of a new server or two and all the gymnastics that go along with that.
Even Brandywine, which used to show a queue every night when I logged in has been clear of such waits recently, at least when I have been coming online.
Of course I have no subscriber data, but I wonder why this is. Have all the power gamers hit level 50 and run off already? Is this the summer slump?