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.
My proxy logs for doing a shift-F5 refresh on a local test wiki install include the following get/response headers for Firefox:
======================================================== +++GET 1595+++ GET /wiki/skins/monobook/main.css?55 HTTP/1.1 Host: 192.168.0.64 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1 Accept: text/css,*/*;q=0.1 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Referer: http://192.168.0.64/wiki/index.php/Test Cookie: wikidbUserName=Nickj; wikidb_session=178df0fe68c75834643af65dec9ec98a; wikidbLoggedOut=20070208020154 Pragma: no-cache Cache-Control: no-cache Connection: keep-alive Browser reload detected...
+++RESP 1595+++ HTTP/1.1 200 OK Date: Thu, 08 Feb 2007 05:02:41 GMT Server: Apache Last-Modified: Mon, 05 Feb 2007 23:57:09 GMT ETag: "709d-428c37389ff40" Accept-Ranges: bytes Vary: Accept-Encoding,User-Agent Content-Encoding: gzip Cache-Control: max-age=2592000, public Content-Length: 7763 Content-Type: text/css +++CLOSE 1595+++ BlockList 1596: in Bypass, line 69
+++GET 1596+++ GET /wiki/skins/common/commonPrint.css?55 HTTP/1.1 Host: 192.168.0.64 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1 Accept: text/css,*/*;q=0.1 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Referer: http://192.168.0.64/wiki/index.php/Test Cookie: wikidbUserName=Nickj; wikidb_session=178df0fe68c75834643af65dec9ec98a; wikidbLoggedOut=20070208020154 Pragma: no-cache Cache-Control: no-cache Connection: keep-alive Browser reload detected...
+++RESP 1596+++ HTTP/1.1 200 OK Date: Thu, 08 Feb 2007 05:02:41 GMT Server: Apache Last-Modified: Mon, 05 Feb 2007 23:57:09 GMT ETag: "1479-428c37389ff40" Accept-Ranges: bytes Vary: Accept-Encoding,User-Agent Content-Encoding: gzip Cache-Control: max-age=2592000, public Content-Length: 1731 Content-Type: text/css +++CLOSE 1596+++ BlockList 1597: in Bypass, line 69
+++GET 1597+++ GET /wiki/skins/monobook/handheld.css?55 HTTP/1.1 Host: 192.168.0.64 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1 Accept: text/css,*/*;q=0.1 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Referer: http://192.168.0.64/wiki/index.php/Test Cookie: wikidbUserName=Nickj; wikidb_session=178df0fe68c75834643af65dec9ec98a; wikidbLoggedOut=20070208020154 Pragma: no-cache Cache-Control: no-cache Connection: keep-alive Browser reload detected...
+++RESP 1597+++ HTTP/1.1 200 OK Date: Thu, 08 Feb 2007 05:02:41 GMT Server: Apache Last-Modified: Mon, 05 Feb 2007 23:57:09 GMT ETag: "5bc3-428c37389ff40" Accept-Ranges: bytes Vary: Accept-Encoding,User-Agent Content-Encoding: gzip Cache-Control: max-age=2592000, public Content-Length: 6631 Content-Type: text/css +++CLOSE 1597+++ BlockList 1598: in Bypass, line 69 ========================================================
... which is also reflected in the apache logs:
======================================================== 192.168.0.2 - - [08/Feb/2007:16:20:38 +1100] "GET /wiki/skins/monobook/main.css?55 HTTP/1.1" 200 7763 "http://192.168.0.64/wiki/index.php/Test" "Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1" 192.168.0.2 - - [08/Feb/2007:16:20:39 +1100] "GET /wiki/skins/common/commonPrint.css?55 HTTP/1.1" 200 1731 "http://192.168.0.64/wiki/index.php/Test" "Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1" 192.168.0.2 - - [08/Feb/2007:16:20:39 +1100] "GET /wiki/skins/monobook/handheld.css?55 HTTP/1.1" 200 6631 "http://192.168.0.64/wiki/index.php/Test" "Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1" ========================================================
Similarly for IE 5.01:
======================================================== +++GET 1610+++ GET /wiki/skins/common/commonPrint.css?55 HTTP/1.1 Accept: */* Referer: http://192.168.0.64/wiki/index.php/Test Accept-Language: en-au Accept-Encoding: gzip, deflate User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322) Host: 192.168.0.64 Pragma: no-cache Connection: keep-alive
+++GET 1611+++ GET /wiki/skins/monobook/main.css?55 HTTP/1.1 Accept: */* Referer: http://192.168.0.64/wiki/index.php/Test Accept-Language: en-au Accept-Encoding: gzip, deflate User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322) Host: 192.168.0.64 Pragma: no-cache Connection: keep-alive BlockList 1612: in Bypass, line 69 Browser reload detected...
+++GET 1612+++ GET /wiki/skins/monobook/handheld.css?55 HTTP/1.1 Accept: */* Referer: http://192.168.0.64/wiki/index.php/Test Accept-Language: en-au Accept-Encoding: gzip, deflate User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322) Host: 192.168.0.64 Pragma: no-cache Connection: keep-alive ========================================================
... which is also reflected in the apache logs:
======================================================== 192.168.0.2 - - [08/Feb/2007:16:21:53 +1100] "GET /wiki/skins/common/commonPrint.css?55 HTTP/1.1" 200 1731 "http://192.168.0.64/wiki/index.php/Main_Page" "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322)" 192.168.0.2 - - [08/Feb/2007:16:21:53 +1100] "GET /wiki/skins/monobook/handheld.css?55 HTTP/1.1" 200 6631 "http://192.168.0.64/wiki/index.php/Main_Page" "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322)" 192.168.0.2 - - [08/Feb/2007:16:21:53 +1100] "GET /wiki/skins/common/IEFixes.js?55 HTTP/1.1" 200 1344 "http://192.168.0.64/wiki/index.php/Main_Page" "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322)" 192.168.0.2 - - [08/Feb/2007:16:21:53 +1100] "GET /wiki/skins/monobook/main.css?55 HTTP/1.1" 200 7763 "http://192.168.0.64/wiki/index.php/Main_Page" "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0; .NET CLR 1.1.4322)" ========================================================
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 ;-)
All the best, Nick.