I know that with AdWords big spenders get their own account managers, but is there something similar with AdSense? Do people who do a lot of AdSense get their own account managers, and if so can you apply for one?
Yes, this is what Premium Publishers receive is an account manager, as well a more flexibility with Ad display. No you cant "apply" it's a case of don't contact us we will contact you.
If your site receives more than 20 million page views a month or 5 million search queries, you are in the running.
I've seen a couple of sites recently who are nowhere near that busy but their ads seem to be set up completely different to most peoples. Would they be abusing the guidlines or can you get permission to do certain things even if you haven't got an account manager?
They could have a network of other sites and their account generates enough collectively to qualify. There is a chance they are running an illegal format, i'd have to see it to be sure. And no, if you are not a premium publisher you have to stick with the normal ad formats. About the only thing you can get permission to do is display your stats without blocking Impressions, CTR etc in certain cases.
Try doing a search for "plumber" here, http://www.vivastreet.co.uk/ The adsense ads look exactly the same as the other listings, they have a different color background when hovered over, and the keyword in the ads is highlighted. Would they have to get special permission to do something like that, or can we all do it?
They are a premium publisher, they have a 10k Alexa see the traffic graph. Regular publishers are limited to the code Google "spits out" when you create ads, you can't modify it's appearance in any way from what's provided.