Their most public attack tool, 'LOIC' [1], uses HTTP requests to try and exhaust a target website's connection capacity. It's a simple attack and the tool is flawed [2]. They're not trying to deny service at layer 3, they're attacking the layer 7 web app. It's relatively easy to detect these requests and shrug them off.

1. http://en.wikipedia.org/wiki/LOIC 2. http://news.ycombinator.com/item?id=1988045

Probably just a BGP thing. The Internet is practically duct-taped together, sometimes the glue gets a little soft.

So far, I have seen no evidence for a 'BGP thing'.

Last i heard, they had 1500 people running their LOIC app. So, not all that much...