[raverbashing]

A weak DNS block is not a "great firewall"

Not sure about SNI sniffing as other commenter mentioned and IP block block (erm) I guess it depends on ISP and it's not so clear cut (everybody does it, especially if there's too much abuse from a certain block)

[CommanderData]

Incorrect not just a DNS block. IP based aswell.

[happymellon]

Only Virgin appear to IP block.

Zen doesn't block it at all.