I upgraded, auto upgrade, no problems!
Horror stories are conflicting plugins – find a bug, then start disabling plugins and RELOADING the page with the bug until it goes away. My only issue with 14 or so plugins active at any given time was with “like/dislike post/comment” (there are two, one for comments, one for posts, and they both conflict with the add post page and previews get disabled/saving drafts cause loss of content).
Other than those two rather superficial plugins, everything including cumulus has functioned great (cumulus marked for 2.7.1, but works OK!)
All in One SEO OK! WP GreetBox OK! Sexy bookmarks OK! Google Integration Toolkit OK!