I have noticed that there is a trend for community-written applets (e.g. shortcutd, tweakr) in the Settings app to be put into a new Extras category at the bottom. Quick Launch previously wasn't in the Extras category but has now been moved there in the latest version after a suggestion in its thread to match shortcutd and tweakr.

I'm wondering if that is always the best thing to do? Is there anything particularly wrong with putting third-party applets in Personalisation, Connectivity, or General? Is there a Nokia-written or community-written policy that says that those sections are out of bounds?

It seems to me that the applets should be located in the section that best covers their functionality, regardless of whether they are provided by Nokia or by third-parties. What do others think?

AFAIK there's no rule for that, last version of BootScreen is a control panel applet and is in the personalization section.