Yesterday it was #8 and currently it is #7 on imdb's top 250 with a weighted average of 8.8. But on its own page it has an unweighted rating of 9.3, meaning that it is currently getting killed on the top 250 due to a low total number of votes. So, if it maintains the score once it has around 100k votes, its weighted average will approach its unweighted average asymptotically and it will take the reigns from Shawshank as The Greatest Of All Time.
However, such an upset is very unlikely. For example, look at the current demographic breakdown:
You'll note that the movie is doing really well with voters under 29. But right now the under 29 bracket represents 78.5% of total voters, and that number is going to drop. For example, if you look at the demographics of Toy Story One and Two, the under 29 bracket only has 51.9% and 49.0% of the overall totals, respectively. Also, US voters are likely to become the minority, which should further push the score down.
But the main problem is that right now, Pixar fanboys are much more likely to have seen the movie, and they are also more likely to enjoy it and rate it high. Once more average moviegoers join the party, they will curb some of the hype.
To give some perspective, The Dark Knight had a 9.6 on its own page and a 9.5 weighted average when it had 69,000 votes. But even The Dark Knight fell out of the top spot less than a month after it came out, and is now #11. So, you expect a rise for the next few weeks, and it may even take the top spot for a very brief time, but then it should fall fairly fast. I'd bet below #15 by this day next year. Toy Story 3 is cute and endearing, but it is certainly not the best movie of all time.