The time for account approval does vary quite a bit, many accounts are approved instantly, while others can take a few days. The exact reason for the variation is something that only DreamHost could tell you.
When your account is approved you will receive an email with log-in details etc. as well as an email confirming your domain registration, if you took advantage of the 'free' domain registration during sign-up.
About the only thing I can suggest is that you sit tight and wait for the emails. I know it's frustrating, but it's worth the wait.
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