What we can expect on day 1: Lots of apps won't work anymore and will need updates which will be trickling out over the next 3 months. http://forums.macrumors.com/threads/macos-sierra-10-12-compatible-apps.1977335/ There will be lots of hidden but severe launch-day bugs which are going to be fixed in the next two service patches. Safari 10 has some nice upgrades (Edit: It came out for El Capitan too.) Picture in Picture mode is cool and works straight away on most sites (by right-clicking twice on YouTube to get the regular video menu, for instance), but there is sadly no transport bar to scrub the video position for "instant replays" of your romantic action movies. Still, cool new feature! But for power users there is already http://heliumfloats.com which works with older macOS versions too. Siri on the desktop will be very fun, for those who have mics. "Siri, play my romantic action movies". Continuity is now even better, but as usual only works for those who have supported Macs (mostly 2012 and newer). I'm contemplating just hanging out and waiting for the first Sierra service patch and for more apps to become compatible... How about you guys? Who will upgrade day 1 and why? Who will wait and why? Please put your votes in the poll too.