There are lots of times when you need some simple password protection, typically via HTTP Authentication, on your Drupal site; my most common use being for publicly accessible development sites that I don't want accidentally indexed by search engines.
There are occasions when you have problems with Internet Explorer (IE) having problems with Javascript or plugins that at least partially stem from the browser's security level, for example it can cause Drupal's Ubercart e-commerce module to not let IE users to checkout (a bad thing). For those occasions, here are all of the IE8 security settings listed out in a single table in all their gory detail.
A small thing I noticed this morning is that Safari wasn't able to complete the DSM 3.0 update - after selecting the file and hitting the upload button it didn't proceed any further. Firefox 3.6, on the other hand, had no problem with the task and was only too happy to process the update. Oh, and the DSM 3.0 OS is gorgeous!