According to this page
Cloud software is slightly different than conventional software. As a general rule, you don't get access to the source code, even if the hosted software is built entirely on open source software. That may not make the software proprietary, strictly speaking, but it doesn't give you all the benefits of open source. In that sense, the benefits of using the "pay for what you use" software as a service model may outweigh the disadvantage of not having access to the source code.
Now OpenStack is bringing cloud support to the open source community, but what about Software as a Service?
Are there any open source SaaS projects out there? Does SaaS even make sense in a FLOSS context?