Hello,
A while ago I realised that that Special:Search behaved differently in different circumstances. It only shows the "search by namespace" radio boxes on searches with search terms - not on plain old Special:Search, or on blank searches. (I am pretty sure the blank search is still the most common query, so this is not as stupid as it might sound.) I just wrote this up as bugzilla:8149.
Anyway, a very nice chap, AmiDaniel, overheard my complaining on IRC and wrote up a Javscript hack that adds the search buttons for blank searches:
http://commons.wikimedia.org/wiki/MediaWiki:Blanksearchextra.js
(see talk page for installation instructions)
It would be good to get a variety of browsers and OSs to try it out and report any problems they encounter. (see talk page) I would like to install it site-wide until the bug is fixed (which is more a matter of someone getting around to it rather than something difficult, I imagine, but IANAD).
regards, Brianna user:pfctdayelise