I had great experience with E Trade and crediting of NW miles to my account(s) over the years. Miles with brokerage companies were tightened after the tech bubble burst and now pretty much everyone charges at least $50 to close/transfer an account so it is not just worth it to do this regularly as before. You may need to call ETrade to "remind" them about the miles but they take care of it pretty quick after the phone call. Do a search here and you will find many comments, a lot of them not fond of this company at all.
One other thing to watch out for is that the Money Market Fund interest rate they credit you is pitiful. I still have one account there that was one of the accounts that I kept moving around in the good old days...Now almost of my accounts are centralized at TD Waterhouse pretty much. There was one deal at Wall Street Brokerage or something like that, not sure if it is still valid...Check Gary's site Finance Section at
http://home.earthlink.net/~pgary/MilesFrame.html
Good luck.