Nitpick: it says that "capacitors are polarized", which is not true in general. There are many kinds of capacitor, some of which are polarized. The electrolyte capacitor in the image is polarized, but I feel there could be a bit more precision in the wording.
Definitely not nitpicking when it's a fact :)
I like spark wifi module. But, I feel it's quiet costly (Photon $19) for some countries (Example: In India it's almost 1200Rs). Mount it on every IoT device will not be cost effective. May be that is one of the reasons, everybody is excited about it but very few are buying/using it.
Now a days, I am working with ESP8266(around $5) wifi module and found it very interesting. It is quiet new, but programming is pain on it.
Edit: ESP8266 price update
http://makezine.com/2015/04/03/esp8266-community-added-ardui...
In the last couple of weeks I've been dabbling with Arduino Uno and Nano and have been very impressed by how plug-and-play everything is.
But I've been super-impressed with the ESP8266. A thumbnail-sized wonder which has a 32-bit CPU, GPIO pins, wi-fi, more RAM than the usual Atmels, costs peanuts ($5) and is available worldwide on ebay and other sources. Now that it has both the Arduino IDE and the nodemcu Lua environment, this little thing is poised to take off. I just finished wiring up a temp sensor to the 8266 using the Arduino IDE. Now I have a tiny temperature web-service on my wi-fi network, responding to a Bonjour/mdns name and it took all of half an hour.
The big IOT unsolved problem is more to do with security and updates.
Disclaimer: My pico arrived the other week.
http://hackaday.com/2014/12/17/esp-gets-fcc-and-ce/
"This announcement does come with a few caveats: the chipset is certified, not the module. Each version of the module must be certified by itself, and there are versions that will never be certified by the FCC. Right now, we’re looking at the ESP8266-06, -07, -08, and -12 modules – the ones with a metal shield – as being the only ones that could potentially pass an FCC cert."