Looking okay to me, I personal would prefer a hotkey driven app with a selection rectangle instead of a on-top form, but thats just a matter of taste.
Small bugs:
- after taking a shot the form position changes/resets.
- setting up a windows protected folder, exemplary "c:\Program Files\", as output folder, app crash.
- you can start your app more than one time. (very uncommon for this kind of tool)
I saw that you also linked source on your Host, will check it out later.