I really liked Xee up version 2.2 and seeing finally a 3.0 released maked me very happy to see continued developed.
Unfortunately i think that the new version is in the current state too slow to be usable like it was on 2.2. I see from comments that some things will not change, but i find that browsing rapidly even on low quality will trigger the loading grain effect very often. Is not really a problem that this effect appears during loading, the problem is that it take a long time to 'recover' from this state, often seconds where i think the application is trying to catch up by loading all the images skipped and in the during this time the application is kinda freezed.
The reduced performances is noticeable when loading a image folder that has as little as 250 images, but is a lot worser for loading archived files: for example a 16 MB zip with 30 images in it will take like seven seconds to load.
(note that my mac is the latest top of the line 27 imac, so i think i can rule out problems from under performing hardware)
I see that you can't do much for fullscreen, but really the osx style fullscreen is awfully bad if you have a multiple monitor setup. A custom solution is probably harder but the actual mode is really a big step back for multiple monitors.
The fact that the application does not do fullscreen in the screen where the window is positioned is a bug i think: at least Preview will use as fullscreen the screen where the window currently resides, Xee always use the main screen (also it moves the window to the main screen when exiting fullscreen).
I hope that some of the issues can be at least reduced, i really liked Xee and i'm more that willing to pay to a new version that can keep up on the performances.