I can tell you that generic QI micro-usb charger pads work fine with the N900. I have one similar to this (has mylar cable to uUSB plug) and use it inside an otterbox case (slight back cover mod w/ a dremel). I use this as a charger at work, and Samsung plate at home.

The connector does take the port up though, and getting it out is a pain. So if you're using the USB port more than once a week for data or misc, this is not for you. If you can't recall the last time you used the USB port for anything but charging, it could still save lots of wear and tear on your connector. (I generally sync and file transfer over wifi or bluetooth.)

One thing to keep in mind is that most pads/plates only supply 500mA to 1A. Some go as high as 1500mA, but that's about the limit right now. Those usually need a 2A brick, since even high-end Qi chargers are in the 70% to 80% efficiency range. (Qi requires 60% for their logo, logoed tend to be over 70%, non-logoed usually in the 40% to 60% range.)

The ones the OP linked above are not Qi logoed. I'm betting they want a full 1A plate to deliver their 650mA current, giving them a 65% efficiency, not bad actually. Put that on a 500mA plate though, and you'll only get 325mA, which may not be enough to even charge an N900. Worse, if your charge plate is crap, you can lose efficiency there too, so it could be less.

Summed up: Yes, they work, but don't skimp if you get it. Get a good high-end pad (500mA min) and plate (1500mA min). Anything less and you may wind up draining more than you charge.