Haven't tried Optimizely but did try VWO (Visual Website Optimizer). It's very easy to use. You just have to plug in their code into your website and start A/B testing by modifying your copywriting stuff like words, images, etc.

The only I dislike about VWO is the amount of features they stuffed into it which makes it quite hard to go through. But overall, if you get to learn it (if you have the time and patience), its a good tool.

Why don't you try Google Website Optimisation?

Yes I have been using optimizely for several clients. Good tool for website performance testing. You can try and see.
Also VWO is another easy to use platform (i agree with seoace).

Thanks

You can also try Marketizator.com...it's a new tool and I'm part of the team.
It's similar to Optimizely and VWO but with more features and cheaper