Fortunately with the release of the 2009 Revit product line the ability to suppress these spaces was included. You can have the spaces suppressed for a single dimension or for all dimensions in the project. To make the change on a project wide basis, go to the settings pulldown and select "Project Units". Click the button next to the length parameter. Click the ckeck box next to "Suppress Spaces" in the Format dialog box. Click OK on all dialog boxes to apply the change.
You may also want to be able to make this change on an individual basis. To do so, highlight a dimension and select Element Properties. In the element properties dialog box, click Edit / New. In the resulting Type Properties dialog box, Click Duplicate, this is so we don't affect this change across the entire project. In the name dialog box, enter a new name and hit OK. Next scroll down and click the Units Format button in the Text parameter group. Uncheck the "Use Project Settings" check box. Place a check next to Suppress Spaces and finally hit Ok to close all dialog boxes. Your dimensions should now look something like this, much better!