We just implemented CE 8.5, upgrading from 8.0, using a rollout plan that I developed. As you can tell by my nickname, I work at a Fortune 100 company where we had the resources to create a swing environment (a duplicate set of servers) running CE 8.5, and imported all our objects from CE 8.0.
I HIGHLY recommend setting up CE 8.5 concurrently (on separate hardware) and importing all objects from the previous version. Doing an in-place upgrade was an idea we examined, but it turned out to cause many problems. A nice clean install created stability that we did not have under 8.0. I can't speak to upgrading from older versions (SI 7, etc.).
Our procedures were fairly complex given our high degree of customization and number of reports, but the installation of CE itself is not that difficult, whether using multiple servers or a single server.
I disagree with the previous statement about Crystal consultants, we employ two and have found them to be of immense value. However, I imagine the knowledge of the individual consultants varies.
-Tim