Lefting 10 days to the runoff election, pollsters are saying the Social Democrat candidate, Aécio Neves (PSDB), is leading for a tiny margin, though his advantage is within the typically 2% sampling error. That is, pollsters are careful to call anything.
If this context holds over the next week, it will be the first time in modern Brazilian democracy that a runner-up candidate in the first round get more votes than the winner, the Workers' Party's incumbent Dilma Rousseff.

The following charts combine the latest polls using the vote intention declared for of the eventual runoff between these two candidates collected over the first round election as priors, the dots at the end is where I believe the candidates will fall. The computation uses the total votes, therefore it includes the Wasting votes as the third category and a residual category of Swing voters. Because I'm using total votes, the winner may have less than 50% of the votes.

This year's election rendered an even more fragmented federal legislative. The way political scientists measure this is by applying an algorithm to calculate the Effective Number of Parties, which is a measure that helps to go beyond the simple number of parties represented in the Parliament. A widely accepted algorithm was proposed by M. Laakso and R. Taagepera (1979): $N = \frac{1}{\sum_{i=1}^{n} p_{i}^{2}}$, where N denotes the effective number of parties and p_i denotes the ith party's fraction of the seats. Few years ago, Grigorii Golosov proposed a new method for computing the effective number of parties in which both larger and smaller parties are not attributed unrealistic scores as those resulted by using the Laakso—Taagepera index. I checked it out, by comparing changes in the Brazilian lower chamber from 2002 to 2014 elections using the Golosov formula: $N = \sum_{i=1}^{n}\frac{p_{i}}{p_{i}+p_{i}^{2}-p_{i}^{2}}$. The results indicate that the legislative power will be more fragmented next year, jumping from 10.5 to 14.5 in the scale.

This is what true vote distributions look like.

Maybe the biggest loser in this election are the polling firms; they once again did a very poor job in capturing the mood of the electorate. Moving from quotas to random sampling design is just the right thing to do.

The latest polls suggest a dramatic recovery of Aecio Neves (PSDB) over Marina Silva (PSB) for the second position. Actually, eve polls are even indicating a slim margin for the Social Democrat, though everything mixes up when considering the margin of error. Essentially, the numbers show that Aecio (PSDB) has been successful in taking back voters he had lost for Marina and that was intensified over the very last days of the campaign. A question that arises is whether the bandwagon effect works for Aecio or not?

Political science theory suggests that when one candidate is reported (repeatedly) winning by a tiny margin, those reports will increase his or her margin (Simon, 1997). As we arrived the last day of campaign with a considerable stock of undecided voters, these reports may in fact produce a snowball effect in favor of the leading opposition candidate.

The box below shows the last simulation output, now including eve polls. By distributing the undecided voters and excluding nulls and white votes, we find a projection of: 45% Dilma (PT), 26% for Aecio (PSDB), 24% for Marina (PSB), and 5% others. The chart below put this as density distributions.

There is a feeling that the Social Democrats may overturn Marina Silva (PSB) this Sunday and advance in the runoff with the incumbent, Dilma Rousseff.
Truly it's the most competitive presidential election since the redemocratization of the country in late 80s, and pollsters are skeptical to call, it's too close. I know election forecast depends on a number of factors and polling data are far from precise everywhere. But, this idea of uncertainty is not knew for me, and I definitely don't like it. Actually, I think it's a really poor job as they can provide more precise information.
The probability distribution bellow shows the margin of Marina (PSB) over Aécio (PSDB) based on the very last polls. Marina is expected to have ~5% margin over Aécio, but the confidence interval ranges from 0 to 10%.