1)
I'm having exact the same problems as described above. After 1.7 you can't save to the default-action video folder. I've played a bit with the save-pathes and it seems that Action! cannot save anything on your %SystemDrive% (e.g. C:\). When i change it to "E:\" it works again.
2)
If you select the recording mode "Active desktop region" and activate "Snap to windows" and select the Context-window (Rightclick-menu), then try to make a Screenshot with the "Capture Screenshot" Button, the result-screenshot shows your desktopwallpaper but not that window. If you use your Action-Take-Screenshot-Hotkey (e.g. F12) instead of the "Capture Screenshot"-Button from the recording-menu, then you have a perfect screenshot of the selected region as is should be.
3)
If you have a Multimonitor-Setup and set the Screenshot Area in the "Capture Screenshots" Optionwindow to "Desktop 2" instead of "Entire desktop", close the app and open it again (of course with adminrights!) the setting is resettet to its default-state "Entire Desktop". Even if you change the value in RegEdit ("ScreenshotsAreaId" from "0" to "1" or "2"), Action resets the Value to "0" after each restart.
Tested on Windows 8 x64 ReleasePreview. I know this is a early beta-OS, but if you want to support the "world's best Windows 8 screen recording performance" you should make it work before announcing it on Facebook or any other Site.