By active display, do you mean it automatically unlocks the display when proximity sensor detects it no longer is in pocket?
(and maybe it also reacts go ambient light change and the motion of taking the device in hand...?)

It doesn't unlock the display once you remove it from the pocket but it lits up the center of the screen with the notification icon and text. The notification icon can be swiped left to open it in app, swipe right to unlock screen or swipe down to clear it instead.

You could also watch some videos of active display on YouTube to get a better idea.

We should have a new update any day now. Might be something new regarding GUI. who knows. It's time for the monthly update. Sit tight.

My 2c. I have thought a lot about the UI so far, without posting, but re: this thread, and first OPs bullet points:
1) I completely agree. The four swipes from the edges of lockscreen and home screen are valuable "spots" for key functionality, and assigning all four to to the ambience switcher is a true waste. The panes/functions behind these four positions should be customizeable and the default should not be "ambience is everything". I for one rarely switches ambience (even if I understand the rationale and motivation from Jolla's side).
Patchmanager is OK, I use it, but in this respect it's far too little and these abilities should be built in.
2) Disagree, but...
3) Again, patchmanager work is under way. I agree that in principle the lockscreen should be locked. But
3a) I want more info there. There's just a lot of wasted empty space. E.g. I want my upcoming calender events and synced tasks there. (Btw: calender and tasks atm suck worse than a black hole.)
3b) some functions could be available on lock screen by pulls, e.g. each notification could accept a sideways pull to open corresponding app. This would be somewhat consistent with the homescreen-"tiles"-sideways-pull-functions.
4) Disagree. As long as the transition does not add more than (tens of) milliseconds to the actual load time, I really like it.

Couldn't agree more. This is a complete PITA. just remembering half-typed messages across windows/sessions, is a must (like N900 had always). Instead of separate windows for each chat: Perhaps an "active chats" switching mechanism that was faster than the go back-find other chat-tap way of today? (on a bigger screen this would be a sidebar.).

does sailfish have full support for working in landscape orientation, and if not, is it planned?

Yes it does. Native apps like the browser, camera and notes all support landscape mode and Android apps also support landscape mode.

Homescreen, settings, etc. are portrait only. In apps landscape is of course supported.

thanks both.

is there any plan to support landscape desktop (homescreen, settings, etc), as well as applications?