According to Sentimentrader.com there have been six other times when the market has gapped up more than 4%. Three of those occurrences were in 1987 and three were in 2008. In every case the gap up was eventually filled and usually pretty quickly.
In 2008 the gaps were caused by similar news to what we have today such as the announcement of TARP. The gaps on 9/19/08 and 10/13/08 were filled two days later while the gap on 10/28/08 took eleven days before it was filled.
The one big difference now is that the market has been in an uptrend until last week and we have this strong tendency toward V-ish bounces. Nonetheless history suggests that this strength fades pretty fast. Chaotic markets usually stay chaotic which is why gaps tend to be filled so quickly