Optimizely has allowed the marketing team to run smaller scale tests without support from the development team, but it has also worked well in larger scale testing where the dev team has had to build the test within Optimizely.
I've heard great feedback from the Marketing and Development team who use the tool. I am not particularly great with code but find it easy to set up tests on my own and feel confident putting them live using the preview tool.
We have mainly used Optimizely for testing. It has been a vital piece of software in our CRO programme and will continue to be as we carry on testing. We have not yet used the personalisation tool but would love to look into this.