Most of the polls have now been published, so I can give the pWPA (political Win Probability Added) for the DNC:
As you can see from the graph, Obama regained all the ground lost after Romney’s RNC bump, and then some. The DNC increased Obama’s pWP by a hefty 50%. Looking at the raw polls, averaging levels of support reported therein, the DNC added 1% support to Obama, and erased .5% support from Romney. You’d think 1.5% wouldn’t be such a big deal, but 1.5% is the typical standard deviation for a large poll. Thus, Obama added a full standard deviation as a buffer between him and Romney, after already having a healthy overall lead before the conventions started.
The next high-leverage event is the first debate, to be held October 3rd. Between then and now I’ll be looking at pWP among the tossup states listed in RealClearPolitic’s map. We should also have enough polls to see how long-lasting the convention effect happens to be, in terms of pWP.