The people at Skyhook Wireless really did a smart job with their Wi-Fi Positioning System: They just use the highly distributed public and private Wi-Fi infrastructure of everyone as reference points for their location tracking. So basically every WiFi-enabled device can use their technology if Skyhook Wireless scanned and located the hotspots that specific area.
I did not find any competitors, yet. Sure, there are companies like innerwireless with their PanGo location management software, or Cisco with their Wireless Location Appliance, or the Finnish ekahau working in the field of Wi-Fi locating technology. But they all focus on closed business solutions where a dedicated infrastructure is used for tracking.
So the Skyhook Wireless WPS solution looks like an innovative and unique way - and an interesting way to realize navigation and location based services in metropolitan areas. Opening up their API for web developers was a brilliant idea - so let’s use it.

No need for handheld GPS devices which do not function properly in metropolitan areas