Played a key role in migrating from an old and busted IT wiki to a much more modern platform based on Telligent. We identified and fixed hundreds of bugs throughout the process, worked with dev team to create a decent user experience / look and feel, and customized dozens of menus and navigation widgets.
To maintain Google SEO earned on the old platform, I ensured that all of the old URLs had a 301 redirect to the corresponding new page (which was important because we had thousands of back links and hundreds of thousands of page views a month on the old platform)
We also implemented dozens of short links to longer URL titles to make it much easier for users to navigate directly to and link to content.
Wiki pages used to be in a very flat format, but during the migration we also created multiple groups that we used to better categorize content and dozens of topic specific forums (vs having one giant forum that had random questions).
We performed extensive testing of the new community in a production sandbox environment 3 months prior to public deployment of the new wiki site. Luckily 3/4ths of issues were surfaced during this beta testing, so there wasn't too much pain after launch. The process was pretty smoothly - in the end we had little downtime and our traffic shot up immediately afterwards due to SEO tweaks and optimizations.
As with all major releases, there were some little things that we had to scramble to address after launch, but I thankfully, I'm reasonably handy with HTML and was able to quickly fix some small issues before anyone noticed and didn't lose much sleep over this.