I doubt the leak will affect HBO too much. It's not like they're going to miss out on advertising revenue. They're a subscription based channel and people will still need to take out a contract to watch episodes 5 to 10. Actually, the only viewers who will have downloaded the leaked episodes will be the pirates who were going to download it anyway. There might be a slight knock on effect with syndication numbers, but I doubt it'll be significant.
BTW, episode 1 has aired in the US. We can discuss that now.