I'm seeing the same issues but I don't think it is the ICS upgrade. I upgraded to ICS as soon as it was released and although I did see a slight decline in battery life, I could make it through the day and still have 20-30% left. Yesterday, I charged my phone over night, went to work and it was almost dead by lunch time. The battery seemed a bit warmer as well. Any ideas on this issue? I did drop my phone two days ago and the battery fell out, but I don't think that would explain this.
I should also mention that I am not using the stock battery. I picked up a larger (3400um) batter and have loved it...until yesterday.