I am sorry to say but there is no such feature available in Google Docs as suchCreate a bookmark (insert -> bookmark). Not only Google Docs but even other services similarThen you can add #name_of_bookmark to Google Docs does not have any such featurethe end of the url.
What you can do is break up your documents into smaller parts and have them stored as separate documents in the same folder.eg: http://docs.google.com/document/d/15xm3Bx4Elnjbg0VNY#name_of_bookmark
This would make editing easier. You can joinis the documents into one when you actually have to give itonly solution to someone elseyour problem, Google Docs does not remembers last position of the cursor or anything lik that.