We provide high-speed Internet access through Embarq. We also have wireless, but keep the router (and the modem) locked up in the owner's closet so that no one will steal it or no smart aleck will try to mess with it.
I don't worry about guests doing illegal things online because the rental company documents who is there and when they are there. So if something inappropriate occurred, we could document that we didn't do it. Actually, just out of curiosity, when we're there, I always check the browsing history to see which websites our guests have been to (and I don't click on ones whose URLs like like a porn site
). Also the websites that they visit give me an idea of if they are truthful about the ages of who is staying at the house. BTW from checking the browsing history, it appears that almost all guests use their own laptops.
After doing this, I clear out the cache, cookies, etc., and update the virus protection and anti-spyware. If the guest totally messes up the desktop, in the owners closet we keep copies of the operating system, MS Office, McAfee, etc., and just wipe everything out and reinstall the software.