Do you edit plugins?

Hi all
I have a friend who uses wordpress for all his web dev. I’ve noticed that he often has to tweak the plugins he uses to get them to work exactly as he needs for each site.
This makes perfect sense, as plugins can’t be all things to all people.

This brings me to my question: How often do you need to alter plugins that you have on any of your sites? And if you do alter them, does that stop you updating (or at least make it much more difficult when you have to)?

I am just feeling the water, as I thought I might write a plugin that keeps track of what files you have edited for what plugins, so you don’t accidentally overwrite any changes you have made.

Any thoughts or feedback welcomed 🙂