My girlfriend has a 38mm Watch. I updated it to 1.0.1 as soon as the update was available and everything seemed OK. However, the following day her battery life had dramatically shortened. Before the update her battery life had never dipped below 35%, for a typical day from 6.15am until 10pm. The day before yesterday, after the update, she got a low battery warning at about 7.30pm when the battery level dipped to 10%. Today the phone has gone into power reserve mode, at around 6.30pm. Not sure if the OS update is responsible for the sudden change in battery performance, or whether it is a coincidence. I have a 42mm Watch which I updated to 1.0.1 at the same time but my battery life has not changed, and is still great (never dropped below 40%).