Not the Best Seat in the House
Yes, sometimes people accidentally walk in on the bathroom when it is occupied. To avoid any unnecessary embarrassment, try to ensure the toilet is screened from immediate view in some way. In addition to using the edge of the cabinet or vanity as a block, you can add a simple wooden screen or semi-translucent panel of etched glass to do the trick.
Your Biggest Fan
Ventilation is extremely important to consider when you are remodeling or finishing a bathroom. Good air circulation will keep humidity down and prevent the likeliness of mold growing. It's so important, in fact, that many states have building codes that require the installation of a ventilation fan that circulates a certain amount of air per minute.