Google's web accelerator is easily the most controversial "enhancement" to the current technological infrastructure of the web since VeriSigns abominable Sitefinder. Web apps are breaking left, right and center due to overzealous prefetching. Reports aren't in yet on the extra bandwidth cost for content providers incurred by same prefetching.
And furthermore it seems the application itself is a mess, sending different people the same cached session dependent cached pages from webapplications.
[UPDATE: This problems may only be a problem by appearance, as reported here]
As is written down all over the place, the broken webapps are probably not coded in true RESTian fashion but breaking them seems to be a violation of the 'liberal in what you'll accept, strict in what you send' philosophy that keeps the entire internet running.
This wouldn't be so bad if it was just happening to a few people, but this is backed by Google. It's like if the biggest automaker in the world promised all customers a free exchange of their current car with a Hummer or some similar "I Own The Road" gas-guzzler. A nightmare.
Alternate fave analogy: It's like Mr Burns planning to block out the sun so his nuclear plant will make more money.