I learned Autocad 14 on my own machine across a couple of months. Customized my input tablet and keyboard shortcuts to make my common tasks easier.

Then I went to a machine shop to have my widgets built, and tried to use their Autocad - and I was completely helpless, asking "how do you ... ?" for the most common tasks. I never bothered to customize key-shortcuts again, I don't work alone on a single machine enough to make it worthwhile.