I'm pretty sure most of them don't.
My resume is either still out there on some "jobs" web site somewhere or it's been sold/shared between recruiting firms as I still get one or two "cold" e-mails a week from a recruiter; I haven't been "looking" for 5+ years.
In mine, near the beginning, it says something to the effect of "If the responsibilities for your position include the words 'Microsoft' or 'Windows' anywhere, I am not interested in the position. Please do not contact me."
The last recruiter e-mail I received, two days ago, says:
> Your profile came up in my database as a possible candidate that might be qualified for a new Windows Systems Admin I received in my office this morning. My client is with the Department of Defense and is looking for someone with a MSCA [sic] or MCSE or higher for this role.
I believe the overwhelming majority of them don't look at them at all. They punch a keyword or two into their database, then, like spammers, blast the same form e-mail out to anyone whose name comes up.