A pilot script was completed late last year. It passed GRRM's seal of approval and was sent to HBO. HBO apparently started doing some cost calculations on possible budgets. I also believe that there was speculation that HBO might just do a pilot rather than do a full series, which would be unusual for HBO (they normally commit immediately to a full season), but if the budget is high it might be the way they go.
There was some hope that whilst the Writer's Strike was ongoing that HBO might be tempted to put ASoIaF into pre-production, since they already had a fully-completed pilot script to work with. However, that didn't happen and apparently they're looking at a 'rival' King Arthur mini-series as well. I imagine that there will be some more news on this in the coming months.