Very involved and not user-friendly...
We have been using CiviCRM for the past 6 years. We've worked with a couple different consultants (hiring someone is necessary when working with this open source software) and spent thousands upon thousands of dollars having it customized for our needs, and it's still not a user-friendly experience for our end users. On top of that, we've encountered multiple bugs (some cost thousands of dollars for us to hire our consultants to build patches for, since this is open source and there's no official support). It's not all bad, and I think it might work better for certain organizations than others (we're a trade association, fwiw). All in all, I wish we could go back in time and try another option...