if you investigate further, you'll find that it's not quite that simple; some things work, some don't, and some _sort_of_ work... yep it's a mess. there's work being done on it, though...
in the meantime, for most things, like changing your search pref, you may find that using togglepref() with a single value works the way you would expect setpref() to... it works for me, anyway.