True, Janus.
I have said that Yoda was surprised in Palpatine's office, but he did bring his hands up in a last ditch effort to defend himself. But he was overpowered and smashed against the wall.
Also. Both our main villain and our uber Yoda don't like to pay attention with one another. For example:
Incident A:
Sidious raised his hands very slowly, and Yoda simply stood there. If I were Yoda, I would cleverly deduce that when I walked into my enemy's stronghold - this enemy being a Sith Lord, also - I would deduce that he would be a severe threat to my life and that he would attempt to attack me whenever he could. I would cleverly deduce that, being Dooku's old master, he would also know all - and even more - of Dooku's tricks. Like that old Sith Lightning technique. Thusly, I would defend myself should this cowled Sith Lord ever raise his hands at me, assuming he would chuck lightning at me, and not attempt to give me the finger.
Incident B:
Yoda caught a pod - in front of Sidious's own open eyes. Sidious then decides to break into a jolly good laugh, assuming a little green elf catching a pod quadruple his size must be immensely humorous. That same Sith Lord then apparently forgets that his opponent is immensely deadly, and possesses the desire to kill him. So he decides to not pay attention, despite the creature having a very heavy blunt object that could be used to crush vital bones and organs that the Sith Lord is required to live with. Thusly, it is my belief that the Sith Lord should've simply shook his head and chucked another pod instead of enjoying a good laugh at an inconveniant time.