@chaley: My intention is to make saved searches less discoverable. There are virtual libraries that perform the same function in a much user-friendlier manner. The only case where saved searches are useful is if you want to use both VLs and Saved searches. And for such use cases (which are relatively rare) the tweak exists to restore the saved search box.
As for the button to hide the search bar, if you dont want to use it, simply ignore its existence. The search bar defaults to shown.
My overall concern with these changes is to de-clutter the UI a bit to make it more obvious what are the main functions of calibre, while still allowing power users to use the power tools relatively easily. It doesn't have much to do with small screens, although working better on small screens is a nice bonus.
I dont think this change is on par witht he chage to remove the search highlights button. The hide search bar button basically works just like the hide tag browser/etc. buttons. And while we do get the occasional post from someone who has hidden one of the panels and cant find them again, it is not nearly as bad as for search highlights. Not to mention that, IIRC, the problem with the search highlights button was much worse before that button was hidden. People would keep clicking it and not knowing why their searches were not filters any more.