Excel 2010 reinvents the conditional format for data bars. We now have more control over the conditional formatting as a whole and not only databars; however, with data bars we now have the option to plot negative values as well.
Here’s how it looks like:

Figure 1: Excel 2010 Conditional Format Data Bars
Once we apply one of the built-in conditional formats for data bars, we can access the Conditional Format Manage Rules dialog box in order to edit the new conditional format rule:

Figure 2: Determining Negative Value and Axis...
Finally, you can determine various aspects of how the value are displayed as well as the axis:

Figure 3: Determining data bars aspects such as axis settings