Oh good heavens, Norwex. I have encountered these magic cloths, and as you might suspect, they are a scam. First of all they are nothing more than microfibre cloths. If this is what you are looking for get some from Costco; the price is around 1/10th of what you will pay to Norwex.
As for the silver angle, this is something new they just added to their product in the last few years, presumably because overcharging people for plain microfibre was becoming a little transparent. There is almost no plausibility argument here, and there is no research suggesting that having colloidal silver inside your cloth has any antibacterial properties. Norwex themselves will produce a few "studies" if asked about it, but they are crap and in no way demonstrate what they are claiming.
At the end of the day this is just another MLM scheme. My wife went to one of the presentations and related the following anecdote:
The salesperson at the presentation takes a raw chicken breast and wipes it on the counter. Then she wipes the counter with a Norwex cloth. Then, she wipes off her own hands with the same cloth, and proceeds to lick her fingers. And that's it. That's your sales pitch. She shows you how much she believes in it; of course you have no idea if she just got lucky, or even if she gets uncontrollable vomiting the next day, but at least she trusts the product!
Stay away from this stuff, it is obscenely overpriced. If you're looking for microfibre, go to Costco.
Also, I will now type Norwex a few times so that this post will show up in a Google search and we get the sales reps in here to defend their ridiculous product. Norwex. Norwex. Does Norwex work? Norwex.