That's six CSS files for most desktop browsers, and seven if you're using IE.
Actually just four and five, respectively. The media-specific stylesheets will probably not be loaded by clients that aren't using that medium.
I can only speak to what Firefox and IE are actually doing.
[snip]
I.e. both browsers fetch all 3 media variant stylesheets, at least on a full refresh.
... and exactly why both browsers feel the need to load a media="handheld" stylesheet whilst running on a distinctly non-handheld device is a question that's probably best directed at the authors of those browsers ;-)
Have you filed bug reports with them? :)
For Firefox: See: "Bug 79021 - All stylesheets are loaded regardless of rendering media" https://bugzilla.mozilla.org/show_bug.cgi?id=79021 [Open 5.5 years, no activity in past 3.5 years]
For IE: Don't care - reporting bugs to MS is an exercise in pain and frustration, involving having to provide your credit card details to do their QA for them on their products (and then they say "sorry, we can't help" - completely useless), or if you use the web feedback forms they just ignore you for 9 years (at which point they discontinue the product) even though it was clearly a 1-line trivial fix ... or at least these have been *my* experiences reporting bugs to MS. And as the piece-de-resistance, their IE bug database is now closed ( https://connect.microsoft.com/IE ) to both reads and writes. Nope - I'm leaving this one to a masochist.
All the best, Nick.