Realm connections have been put on hold until further backend work can be completed. Community Manager Nethaera let everyone know about this in a post on the official forms yesterday. This represents a deviation from what it has been like over most of the past year, with new realm connections happening every week or so.
However, recently the connections have ground to a halt as Blizzard works out various issues. While there has been little said about the issues by Blizzard, there have been numerous and credible reports of problems arising because of the connections -- everything from players not showing up in the zone correctly, to Auction Houses not working. For the most part Blizzard has been able to take care of these issues after a connection has been made, however the bumpy roll out still remains.
There is no indication as to when the connections will resume. Nethaera's full statement after the break.