Apparently, this is the market of the never-ending bid.
After the market basically went straight up for the entire month of January, a number of market players were anticipating that the indices might take a rest. We had four straight days of mixed action to end January, and it looked like we might be weakening, but it turned out to be a bear trap, and it was sprung today.
What made today particularly impressive was that the upside move picked up steam even though there really wasn't any real catalyst for the strength. Economic reports were mixed, Greece continued to promise it would have a debt deal any minute, AMZN's earnings were unexpectedly weak, and there wasn't any real positive headline news. In the perverse manner of the market, that probably helped to keep things running, as it increased the fear of being left behind.
Although we have had a number of runs like this in recent years, these markets with the never-ending bids are not as easy as they look unless you just buy and hold and never have an interest in selling an extended stock.