Yeah, after half an hour of waving your arms about I'm sure even the most enthusiastic user would start to feel tired - let alone the 8+ hour grind many of us desk jockeys endure daily.
Would it be a useful supplement? Certainly, I can see the novelty in, say, closing applications with a handwave (although, oops, I was just waving at my colleague behind my desk), or launching a browser window by making a wanking motion. Ha. But as a replacement for heavy duty daily work? Not likely.