I fiddled a bit for making my VIM tell me when obvious (statically detectable) mistakes sit in my code when saving. This speeds up the testing process a bit when e.g. syntax errors exist and helps me adhere to PEP 8.
We were embedding a spinner to give user feedback while loading data from a server which might take a little longer (but can also be pretty quick in most cases).
Implementing the spinner itself isn’t that hard, but we found that quick responses from the server caused visual artifacts flickering up because the spinner was only visible for a few milliseconds (probably roughly 30ms).