I have run my site for 13 years now. I have been on page 1 of Google for 9 of those years. I have been on Page 1 placement 1 out of 64 million search results for 8 of those years.
My site is static, handwritten content. I have avoided WordPress, Joomla, Drupal, and all the others when it comes to key pages:
1) My home page
2) My static unchanging content pages (the main core of the site)
These pages *might* consist of 30 to 40 pages maximum.
I then tacked on PostNuke (many years ago) for a news section.
I then tacked on vBulletin for a forum.
I then tacked on Magento for a store.
So my site is static, with plug-ins (basically). This has served me well, and I often tell myself that I ranked so well for so many years because every bit of my code on the core pages, was 100% unique and hand written from scratch.
Now its 2013, and my users want a global site login. My site needs to work on mobile platforms and ipads. My site needs to use HTML5 because I'm told thats the wave of the future. My users want to post images and participate on the forums and purchase products with one login.
So I am terrified ... but im thinking about a CMS system. I dont want to drop vBulletin and I'm not dropping Magento. I need something better than PostNuke for the news center. But do I really need to go 100% CMS? Probably not. Probably can still have a static home page and static core content while carrying a logon session right?