The Invesco QQQ Trust has been a big winner -- but it has also been a big loser. The Invesco QQQ Trust (QQQ -0.39%) has turned a $10,000 investment at its inception in March 1999 into $125,000. Its returns handily outdistance the performance of the S&P 500 index over that span. Given that backdrop, it seems like this could be the millionaire-maker investment that you've been looking for! But don't rush out to buy it -- there are some pretty big caveats to consider. What does the Invesco QQQ Trust do? The In ...