After a previous reworking of MediaWiki’s stylesheet-handling code to allow adding handheld stylesheets, I’ve gone ahead and implemented bug 2889 adding per-site customizable MediaWiki:Print.css and MediaWiki:Handheld.css pages.
The ability to specify some handheld tweaks is needed to be able to work around issues with certain kinds of layout formatting, especially the big beautiful multi-column table layouts which are popular on portal and main pages.
While lovely on a large screen, on a small device they tend to either make the columns reaaaally tiny or push things out off screen. On English Wikipedia I’ve thrown in some quick style hacks to flatten out those tables on the main page (this was applied already by Opera Mini’s classic view, but not Opera’s other browsers in small-screen mode):
There are still improvements that can be done, but it at least helps things fit on screen! MediaWiki:Handheld.css can be edited on each of our wikis to tweak things up as desired/required.
Of course it’s always best to try to use clean, scalable styles that work on small screens to begin with. :)