Well...
While I do like people that people here are using arguments from an empirical perspective (things seen in the films), let me just add some EU literature stuff:
a)
Yoda is able to avoid hits from three Council level Jedi trying to hit him without using his lightsaber. And one of those was Depa Billaba who is a Vaapad master. I doubt that Dooku alone would be able to kill him in a lightsaber duel and as we have seen that Dooku isn't able to overwhelm Yoda with force powers.
b)
In Dark Rendevouz we can see how much respect Dooku has for Yoda and from that perspective it's very questionable if Dooku really thought that he was more powerful then Yoda (which he says in AotC). That might be some taunting (Dun Möch).
c)
According to more EU stuff Yoda mastered something called "Tràkata" which means dodging enemy attacks while having a deactivated lightsaber in hand and then switch it on, sending it to the enemy body with the intention to hurt somebody badly or even kill him. He didn't do that against Dooku even though he could have done this (count his effective parries against Dooku).
Back to the empirical perspective and some speculation:
1)
For what we can tell, Yoda didn't want to kill Dooku but disarm and capture him. I don't have any other explanation for Yoda not using the force in an offensive way against Dooku (e.g. throwing the things back at Dooku that Dooku threw at him). The only "aggressive" action was throwing Dooku's force lightning back at him and this was definately not done with the intention to kill Dooku.
2)
We have seen what Yoda acts like if his intention is to kill somebody. In ROTS when he fights against the Clone Troopers he's more aggressive then in his fight against Dooku (force pushing them around, throwing his lightsaber to kill them). Same thing when he fights against Sidious (force pushing him across the room and he fights even more aggressive - or let's say less acrobatic - against Sidious).
3)
If you just count the number and effeciency of attacks in the AotC fight you will see that Yoda is constantly hammering on Dooku's defence where Dooku's counter attacks (and he's a master of those) are effectively only hitting the air where Yoda was some moment before. It simply looks like Dooku isn't able to threat Yoda's life with his lightsaber skills.
Conclusion:
Yoda possibly didn't went all out on Dooku because he didn't want to kill him while we can be quite sure that Dooku wanted to defeat Yoda and using everything he can - and he still lost or was thinking he had to flee (thereby he at least indirectly admitted that he can't take Yoda). So if Dooku can't defeat a Yoda that was most likely not using anything he has against Dooku, how can he hope to defeat Yoda when Yoda comes up with the intention to kill him ?
Originally posted by Admiral Akbar
He did block it on later into the fight. After his lightsaber was blasted he was prepared, but the first time Sidious blasted lightning yoda was indeed not ready. Take a look at the picture. Also, Yoda could not have expected it since he cant read Sids mind. And lightning does not travel slow.
a) Yoda waltzed into the lair of the Sith Lord. While Yoda may be one of my very favorite characters, it was damn ignorant of him to do what he did. So Sidious zapped, and Yoda got sense knocked back in him.
b) No. Lightning doesn't travel slow. But if you'd kindly note the speed at which Sidious raised his hands, you'd notice that it wasn't an effort on his part. What did Yoda think Sidious was going to do? Give him the finger?
Originally posted by Sorgo
Dooku could possibly defeat Yoda, but honestly... I doubt it. It would be a long fight, but I don't see Dooku defeating Yoda.
Well, if even Sorgo is willing to admit Yoda's win... does anyone actually think the odds are in Dooku's favor?
Borbarad, for once I will thank you, for supporting (perhaps unintentionally, I don't know) what I said about Yoda not wanting to kill Dooku.
b) No. Lightning doesn't travel slow. But if you'd kindly note the speed at which Sidious raised his hands, you'd notice that it wasn't an effort on his part. What did Yoda think Sidious was going to do? Give him the finger?