Your website is as much a part of your total corporate identity as any more traditional aspect has always been. While most business oriented sites should avoid looking silly or immature, don't fall into the trap of becoming so 'stuffy' and humorless that you lose your warmth and approachability. It's always important to remember your visitors' comfort level. Remember that less is more. Don't overwhelm your visitors with a sea of dancing animation, volumes of text, or over-done frames.
Simplicity is elegance.
Offer them something they can't get elsewhere - be it a valuable tool, or often updated information. Because traditional print media is a finite product that can only be replaced rather than updated and tweaked, many business people are not prepared for the after-care tasks that exist with their new site. If your company has someone trained in the field to do updates properly, always remembering that the site is a total structure with design to adhere to rather than a piece-meal operation, then you may be successful in handling your own maintenance and updates. But usually the reason your firm hired a professional designer in the first place is because you realized that you did not have the capabilties in-house. Little by little, page by page, the site's beauty, elegance and professionalism breaks down.