Sending drafts to readers/editors

seanan_mcquire asked a question in post about first/second/third readers.

I'm always fascinated by the way different people approach the editing process. I know authors who don't let anyone see anything until the book is finished for the first time. ... What are your feelings on editing? How much is too much -- and how mean is too mean?

I am one of a few writers I know who did not come to craft through workshopping. I didn't come up through fanfic critiques, which are often the same thing; I wrote -- badly -- and I put things in drawers (literally, although these were file drawers) for a very long time. I had no experience with the paradigm of improvement through critique until I ventured into workshop-style classes.
( yes, this is another quasi-process post! )