I'm interested in offer my clients cloud hosting, however I wanted to know the following:

1. What software do you recommend for cloudhosting (o/s, setup) such as OnApp, OpenStatck, etc?
2. What is CloudLinux really for?
3. Has anyone used OpenStack or OnApp?

Thanks.

I've been planning a deployment with OnApp for a few weeks now. So far they've been very helpful with answering questions and their software seems to be really great to use in all environments.

CloudLinux isn't actually a cloud hosting platform, it's just a Linux OS.

Can't comment on OpenStack but more and more providers are starting to use OnApp. Some big ones like VPS.net have been achieving great success with OnApp :)