If I'm doing a small commercial job (I only ever take on small projects) I'll always use/create my own mini CMS - that way I'm selling my own work and not someone else's.
My CMS has a template engine, so the most I need to do is whip up a few HTML templates for whatever functions the client wants (news page, gallery etc). The handy thing is once I've developed a feature such as a news page, I keep it in my code library so I can use it easily on another job.
I enjoy coding and I'm always looking to develop my skillset, so I tend to create my own scripts and classes. However sometimes when I'm in charity-mode and someone needs a hand, I'll just hook them up with an open source CMS and leave them to it.