I have found similar instructions recently, and used them successfully, but I have a couple of tweaks to suggest:

1) Google recommends (http://mail.google.com/support/bin/answer.py?answer=78892#) that you leave "Store sent messages on server" OFF. This works for me; if you are using smtp.gmail.com as your outgoing server, messages will automatically go into your Sent folder.

2) I do not like setting a path prefix (Some people like to set it to "Gmail"). In my experience, it cuts off access to my other Gmail labels/folders.

3) I leave the Trash mailbox alone, but I do click on my /Gmail/Drafts folder and set "Use this mailbox for: Drafts".

4) If you have already been using your Gmail account in Mail, using the "Use this mailbox for" option will delete your existing local folders such as "Sent" and "Drafts" -- AND the messages therein. So I make sure to have a backup of each of those.