OK, here is my summary after using WP 8.1 developer preview ever since it was released on my HTC 8S.
I've done hard and soft reset multiple times, last time was 4 days ago
Bad (Bugs, problems etc.):
1. Internet explorer crashes when loading heavy websites (Phonearena.com for example). It doesn't crash immediately, maybe after a minute. Also when browsing the wpcentral forums it tends to continually refresh the page until it crashes. I've noticed that a lot of other users seem to have this problem (The ones with HTC phones, but some with lumias too). This problem occurs in other browsers too but not always (Maxton works fine on WPcentral forums)
2. I can't acces Internet Explorers advanced settings. Not from inside the app, neither from the settings menu. It just returns me to the previous screen.
3. I can't change my phone language to English (US). I have found that this happends on other HTC phones too
4. Animations stutter sometimes.This never happened in WP8, but mostly the phone operates smoothly. It's not a biggie since it happens rarely, mostly after an app crashes
5. App loading times are hit or miss. This has nothing to do with where the app was installed. Sometimes they load faster, sometimes slower. WP8 was pretty much consistent when it came to this
6. Sometimes live tiles take a second or two to "load".. This mostly happens when I unlock the phone and scroll fast to the bottom. This never happened on WP8
Conclusion:I think that there are some RAM memory management problems. It's the only thing that could explain most of those problems. I'm getting a feeling that they still haven't finished tweaking the new memory management system.
The good:
1. Everything about WP 8.1. I admit, there are some problems, but the OS feels really mature now. I'm liking the app2sd option especially (Storage was a big problem on HTC 8S).
In general I don't understand all the complaints (Ok, the new cursor for text selection is bad - it's the only one agree with). We even have file managers now
, action center, tile backgrounds