To be sure, there are arguments against shutting down computers, but they aren't particularly convincing.
1. The extra startup and shut-down time is a waste of productivity: C'mon, few of us are truly productive every minute of the day. Switch on your machine before you get a cup of coffee or chat up the girl in the neighboring cube. If you can't wait five minutes in the morning, loosen up your schedule.
2. The computer needs to remain in standby for maintenance and updates: Schedule the updates for times during the workday when you are at lunch or on break.
3. I demand the convenience of a quick return from standby mode: See No. 1. Even if you can afford the added utility bill costs, the environment may not be able to.