hi robbero, great questions.
ok so let me try to address a few:
1. i'll have to take a look at how picpick does it -- one of the things that makes screenshot captor slower at doing autoscroll is that it's trying a few different methods and doing horizontal and vertical scrolling. it's not perfect and i've been meaning to see if i can improve it in a variety of ways, i just haven't gotten around to it yet.
2. open with screenshot captor -- i think i know the problem and i'm putting it on my todo list -- if i remember correctly screenshot captor expects folder paths to be passed to it on the commandline, not filenames. should be an easy fix.
3. you can super easily change the file format of the current image by adding the new file extension for the format you want to the file name part at the bottom left, and hitting enter. the file will be converted to the desired format and will stay in that format. (if you want to save a copy with a new format use the "File -> save copy as" menu command).
4. you can change the "After Capture Show" action quickly from a right-click in the Screenshto Captor system tray icon menu.
5. you can disable the autosaving of images. you'll find it as the top checkbox on the "Saving and Loading Files" tab of options.
6. short answer is that the thumbnail panel performs horribly with so many images. the only current fix for this is to do what i do (and what i think is the smart thing to do for a variety of reasons), which is to create subfolders in your screenshots directory and file things away so you dont have more than a hundred or so screenshots in each folder. Screenshot captor has a ton of functions to help you auto file screenshots by date or move screenshots around, etc. to make this painless. Personally i think its a good thing to do to keep things organized.
6. long answer is that in the last 2 weeks i've been working on a related project and finally took the time to implement the thumbnail browser i always intended for screenshot captor. it looks nearly identical but the internals are completely different, which makes it much much more efficient at handling file system changes and updates. i still have to test it on huge numbers of screenshots, but it should be a lot better, and i will eventually integrate this into screenshot captor. it may solve a whole host of these thumbnail panel flickering things in SC.