- no more "Newer> Newest>>" links to jump to the most recent comments when there are more than 200 on a post. Instead, the most unfriendly "load more..." link will have to be use as many times as there are pages to bring the latest comments. Of course this wouldn't be an issue if Blogger had an option to show the new comments on top.
- embedded comment location restricts customization: e.g. comment numbering scripts don't work in that mode.
- it may require to "revert widgets template to default" or "repair" your post template in order to start working.
I'm normally an early adopter of anything new from Google (except Google+), but I'll pass this one for the moment...