I found the whole process to be very easy, you call 0800 800 123 from your mobile, tell them where you live, and that you want broadband, they give you the options, you pick one, and that's it. The more you pay, the better it is.
As part of my work, I've had to speak to several isps for customers, I've found them very helpful, more so in the uk.
I've went for a half meg connection, and performance is fine, downlands of movies and tv shows from newsgroups are very fast. (Tv is rubbish in NZ, I don't want to wait months to watch Dr Who). Only problem I had was when watching streaming video from some servers in China (live sports, until I get sky installed), the performance was quite poor.
I may upgrade to 1mb when we move house and start doing video conf stuff, or sign up with skype.