Since I'm in the process of migrating an existing site to Flexicontent, I thought I'd share my observations and suggestions about the process. I'll add more to the thread if I come across anything else.
The ability to migrate existing Joomla content of course is extremely helpful. But a couple of changes could help save a lot of time I think.
Uncategorized Content. The migration doesn't include uncategorized content. Perhaps the solution would be to have Flexicontent automatically create a new "uncategorized" category and bring this content into it.
Menu Items and duplicate article creation on migration. The bigger the site, the longer it takes to transfer menus from core article types to flexi items. Secondary issue exists on non-SEF sites as all urls are now different because of the item and article id changes.
EDIT: Actually, even the urls on sites with SEF enabled will also change whenever the "alias" has been modified. Obviously, this means incoming links to the old URL's will be broken unless the alias's are all updated or 301s are added.
Is there a way to allow menus to stay as standard Joomla menu types? Are duplicating articles and creating new itemIDs/articleIds necessary for the migration? Except for possible performance issues, the front-end redirect seems to work ok... You mentioned about hits being duplicated (Emmanuel), but I personally never use hits and I'm probably not the only one
Article Binding. After migration, articles weren't automatically binded for me. Not a big issue, but just FYI it did take a little head scratching and clicking around the control panel to get the message offering to bind the articles. I'm sure there's a good reason for this, but if you can't (or don't want to) automate this, it might be helpful to others to provide a tip after the migration about what to do.