Hey Giles,
I recently upgraded to 1.7 and most things worked fine, but there were a couple issues that were real deal-breakers and I ended up down-grading.
I don’t know if it’s just my own setup or what, but my ‘Invite Anyone’ plugin stopped working. My site has registration deactivated, but normally Invite Anyone allows invited people to sign-up anyway. This stopped being the case after upgrading to 1.7. Also, my top bar disappeared after upgrading and reappeared after downgrading.
Again, not sure if you’d have the same issues, but that’s what happened on my site.
Hope that’s useful!
Dan