I saw Clash of the Titans not too long ago in 3D. My opinion on the movie:
I would recommended it as a decent movie to see. Personally, the movie moves pretty fast for my tastes. Sometimes it can be difficult to keep up with the plot if you're not paying attention.
The 3D effects were absolutely and utterly terrible. I took off my glasses at many many times during the movie and saw absolutely no difference in the picture, except that it actually looked better. Even the credits had no 3D effects at all! I was very disappointed and never noticed anything 3D, not even an extra depth in the movie at most times. Any time there was that I noticed, it wasn't even anything interesting like a fight scene. If the fight or monster scenes had them, they were very subtle.
I'd recommended going to see it for the heck of it, but see it in 2D to avoid the strain on your eyes, the extra fee, and the lack of 3D effects.
Happy Easter, everybody!