I used SM from day one (beta 1) until today (beta 2) and found it mostly gimmicky. I've gone back to my original setup that I've been using since 2006.
My original setup:
Hot corner (left): show all windows
Hot corner (right): show desktop
I often drag-and-drop stuff from Desktop into various apps, and SM makes it a slower process.
Here's how drag-and-drop compares:
Stage Manager: Drag a file from desktop and hover it over the desired app for several seconds until the app activates and maximizes its window. Drop.
My original setup: With the desired app in focus, hit the hot corner (right), drag a file from desktop back into the hot corner (right). Drop.
So far, there's nothing better than my 16-year-old setup. I'll let Stage Manager mature a little, or at least wait until its official release, before using it full-time again.