Toggle Wi-Fi to find missing network
While you will not typically hear complaints about the Wi-Fi on most webOS devices, the Pre3 seemed to take a step backward in the reliability of its wireless radio. In addition to a seemingly decreased W-Fi range, it also tends to not show all the available networks that are in range, even if they are previously saved Wi-Fi profiles. This can be an extremely annoying bug that will cause your device to fail to connect to a known network, but it has an equally annoying (although relatively simple) fix. All you need to do is turn Wi-Fi off and then back on again, and all the wireless networks within range will show up again.
If you are a homebrewer, you can also install the "Cycle Wi-Fi in Device Menu" patch in Preware by GuyFromNam that will, not surprisingly, add a "Cycle Wi-Fi" option to the device menu to toggle your Wi-Fi off and then back on. This also appears to work alongside some of the Device Menu expansion patches such as Jason Robitaille's "Device Menu Megamix" patch.