Some Google products contain features that have limited usefulness, when applied to Blogger blogs. FeedBurner has a feature, "Password Protector", which may be useful, to newsfeed readers that support HTTP authentication. Within FeedBurner, we have the "Email Subscriptions" service - which does not support feed authentication. Your readers will be required to use newsreader or aggregator software that supports authentication to view your feed. Some Google, and non Google, services will have a problem, with a FeedBurner protected feed.
What Blogger won't tell you