What's the USP on Optimzely when compared to the already quite formidably awesome Visual Website Optimizer?

Also, as someone that really wants to incorporate this tech into my larger scale marketing efforts I am put off by the pricing models to both of the above mentioned sources.

When only one of several ad campaigns are doing 100k visitors a day you can see how that pricing model does me no good. Particularly when you take into consideration that I never stop testing -something- on a campaigns landing page.

Also would love an API so that something like this could be tightly integrated into my custom conversion analytics solution.

Congratulations on your launch nonetheless.