Alright, I've made a few more modifications.

1. Conditionally editing account references out of follow-up e-mails:
Done, update e-mails no longer contain the "detailed invoice" link.

2. Giving the page a more integrated look with the rest of checkout, including alternate page header('Step 1 of 5', 'Step 2 of 5' etc.) definitions:
Done, no_account looks like another checkout page now.

3. As an optional add-on, a modified tableless order steps mod that will also conditionally display 4 or 5 steps:
Done, you can see this on the test server. The order steps div shows 4 or 5 well formatted steps depending on whether you are checking out with or without an account.

Not done:
A page to check order status with e-mail address and order number.

This is all up on the test server. I'll have it repackaged for download in the next few hours, along with some screen shots from my live store which is a bit nicer looking.

Also of note, I went ahead and took down the forms asking for Company name and fax number. These are still available using the stock Configuration -> Customer Details.

--Joe