You can get it through Comcast as a part of the Internet Plus package ($49.95/mo for me in CA for twelve months and then you should call them to prevent them from upping your rate to $69.95/mo.)
Yes, you can, through third party HBO partners like Pirate Bay and Kick Ass Torrents.
It has many benefits over Amazon offering:
1) It's available worldwide
2) Price is good even for starving students
3) For older seasons, you can choose between 720p/1080i streams and high quality ~30Mbps streams (also known as untouched blu rays)
You can't. I've bought all the episodes through Season 3, but I can't get Season 4 yet, and HBO Go isn't an option because they won't let me pay for it.
They will happily let you pay for it, you just need to have a cable subscription first.
They are going to keep all of their money maker current programming exclusive to their platform for now unfortunately as this is how they currently can afford to make new episodes of Game of Throes for $6 million an episode.
This is a good step though as there is some old content I've been wanting to watch forever which I now can do.
Yeah, you can't. I don't watch cable television, I just use the internet access. So unless I feel like donning a standard cable television package + HBO for $120+/mo I can't get access to HBO Go. It's a shame, I'd certainly be willing to pay for just HBO.