There are many different symptoms and different problems here, so it's impossible to give one set of suggestions that could work for everyone. But here are some general suggestions:
1) Wireless works fine with Linux. Manufacturers usually say that because they are lazy and haven't tested their product with Linux. But if they even attempted to follow the 802.11(alphabet-soup) spec, then they will work with Linux.
2) If at all possible, get to a place that you can access the web (coffee shop or home), and update to the latest version. If no wireless options are convenient, try a USB Clean install
. As of writing the latest official version is 8.2.0 (build 767).
3) If you are having trouble at home, try disabling the wireless security on your router temporarily. If it connect without security, then reenable security with different options. Reboot the XO between each attempt of settings change.
4) If you are successfully connecting at home, but not at a coffee shop, note that there are usually two categories of public hotspots: route based and key based.
Route based hotspots are "open" wifi connections, for which you first connect to the router, then go to their website, login, and their router allows your traffic to flow through. You should be able to "connect" to these without a problem, even though you may not be able to get to your email. Usually the only trick with these is finding a good strong signal with as little interference as possible.
Key based hotspots are those like your home wifi routers where you have to enter a WEP/WPA key just to "connect", which you usually get from the cashier's receipt or something similar. These are far less common, but ironically I've had better success connecting to these.
Unfortunately, I just realized that to this point, all I've said is that they should "just work" without offering any troubleshooting suggestions. Short of poking at it randomly (rebooting, waiting for the mesh to "settle", connecting to one dot then coming back to the one I want) I've also had mixed success.