I've worked for Ipsos Mori in London and Edinburgh, their sister company I-View in Melbourne and also Market Probe in Acton. The job is horrific but easy to get, if you can read you're in! In the case of Market Probe even if you COULDN'T read!
The wages in the UK jobs are seriously low, usually around min wage, in Australia you get an impressive $28 an hour! (about £15) here though like most jobs it's low. Everything the poster said above is true. You will be shouted at, abused and bullied, both by supervisors and people you call. Ipsos Mori Harrow isn't too bad in terms of staff, there are a few bullies running the show in Edinburgh though. Market Probe is really dodgy! The management are hidden in a complex at the back of the building, you aren't allowed there and never ever see them. They also somehow had the bank details of Halifax customers on one particular survey....
Market Probe also only pay in cheque form which is very suspicious! I once did 90 hours for them in a single week. I wanted to kill myself after it but even on min wage that was a fair sized lump of money!
As for surveys themselves they all operate along the same lines. You get called into a briefing, there are shrieks of horror when it sinks in that you will be cold calling people to ask about their bank details at 8pm and then with a sinking heart you reach for your cheap plastic phone.....
The worst survey I ever did was Market Probe, calling US small businesses to ask them about their favourite brands of paint. It was a 45 minute survey, Market Probe equipment barely worked and it was two days before Christmas... fun (!)
A lot of the surveys are health based. I once did a project on eyesight, a genuine question was: "would you agree or disagree that masturbation affects your sight?" The old dear I'd called threatened to call the police and hung up on me.
The one plus point of all this is you can make your own hours! The only plus point!