@Justin Tadlock - You are right.

But I regard any plugin that does only trivial things (which can be easily done manually) as unnecessary. If I had to use a special plugin for every tiny change (e.g. for adding new sidebar/footer links), it would drive me crazy.

I usually tend to check whether the plugin is safe to use - doing that every time a new update is available would be insane. Not to mention dealing with potential incompatibility issues, poorly written code etc - that's really something I'd want to avoid.

I don't switch themes very often anyway. Besides, tweaking my own theme makes me happy. :)