According to a comment from GRRM, principal photography has been pushed back to late July for HBO’s Game of Thrones. Nothing really bad about this, as bringing in so many disparate logistical things together can be difficult, but there’s always the possibility that there’s interesting reasons for it, like having to wait on a newly-cast lead (ala Daenerys) to be free to work, or a director, or other things of this sort.
GRRM also notes that he’s unlikely to spend any time in Northern Ireland to watch the filming, except possibly when his own episode (episode 8) is filmed, and doubtless when he’s in the area for Octocon in October.