I'm designing the front end fro my auction manager system and on my main frontpage, I have the popular "left hand button bar" for navigation. I've read that consistency should remain throughout your site but, if a user logs in to the actual auction manager system and the navigation were to change slightly (to give system options to the user), do you think it would be a major problem?
I really can't see that being a problem if the navigation bar wasn't to change too dramatically and I really don't think there is a better way of doing it too give logged in users extra options. It really depends on how computer literate your target audience will be but I am sure even people with very basic computer knowledge would not be confused by small changes to a navigation bar. Never underestimate your visitors. Many big sites including Sitepoint have changes to the navigation bar depending where you are in the site.