kaled - 5:13 pm on Mar 16, 2010 (gmt 0)
In UK law, a contract may be deemed invalid if it is unfair. You may think this is nuts, but it doesn't change the fact that if a court were to rule that Adsense terms and conditions were unfair then, in theory, Google would have little choice but to make changes.
As to what constitutes fair, that's debatable, however, if the contract does not provide sufficient information for comparison and allows payment rates to be changed without notice, without even being notified at all, etc. then the chances of a court ruling that the contract is fair (and therefore valid) are vanishingly small.