(new Image()).src="http://your.tld/track.png?ua=" + encodeURIComponent(navigator.userAgent);
Update: this is just an example, as ars notes the user agent is sent as a HTTP header. But screen resolution etc is not.
Third parties may wish to store information on the
equipment of a user, or gain access to information
already stored, for a number of purposes, ranging
from the legitimate (such as certain types of
cookies) to those involving unwarranted intrusion
into the private sphere (such as spyware or
viruses). It is therefore of paramount importance
that users be provided with clear and comprehensive
information when engaging in any activity which
could result in such storage or gaining of access.
[1] http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2...
How does this help? The UserAgent is already sent in the headers - what's the point in sending it in a query string?
So, no, these workarounds are not the right answer; we need mechanisms that let users control their data and let them choose to share it. It's up to us as product makers to give them a good reason.
As for mechanisms, to what end, if nobody bothers to use them? Especially things like "randomize User-Agent string" that'd break a great many "non-evil" sites?