I looked through the wiggle database. A TON of their information is super old. Of course there's no way to know how old SkyHook's is since it's totally private.
Skyhook loves to tell you how recent their data is. They re-drive high turnover areas (colleges) a few times a year. Everything else is quite recent. With Skyhook's high profile use in the iPhone they can't afford to be out of date.
Last I checked they had over 45 million access points recorded. With enough users, the system can become self sustaining. You upload all the detected access points in your area for a request so it's trivial for them to auto-update their system if you submitted a newly discovered or changed MAC address.
