From CNN:

According to a new national poll released Tuesday, just before the start of the Democratic convention, the GOP presidential nominee appears to have received a one-point convention bounce, normal for the modern political era.
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CNN’s previous poll, released as the Republican convention got underway, indicated 49% of likely voters backing Obama, with 47% supporting Romney, a virtual tie. In the new survey, which was conducted Friday through Monday, entirely after the GOP convention, both the president and Romney are at 48%.
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Romney gained among independent voters, with a three point 48%-45% margin last week expanding to 52%-42% advantage now.

Now the question remains whether Democrats will get a small bounce, too, from their convention.