Back in January, during the CES, Microsoft said that it plans to release its first Windows Phone 7 update within the upcoming weeks and Steve Ballmer, Microsoft's CEO, became even more concrete when he said, during his Mobile World Congress keynote, that NoDo will be released early March. In preparation for the NoDo update, late February Microsoft has pushed a pre-NoDo update which, as it turned out later, caused some problems on certain Samsung devices while other users around the globe have yet not received the pre-NoDo update. Nevertheless, Microsoft (un)officially rowed back now and has announced via its French Windows Phone 7 blog, that NoDo is now postponed to end of March.
Microsoft has not given a reason yet why it has postponed NoDo but maybe it's related to the update problems it figured out with the pre-NoDo update.
Cheers ~ Arne