I just deleted the contents of the new workspace's folder. Then re-opened the workspace. The imported the prefs. There is the following folder now:
C:\Documents and Settings\asookazian\workspace\testImportPrefs\.metadata\.mylyn\contexts\activity.xml.zip
Here is the contents of the activity.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<InteractionHistory Id="activity" Version="1">
<InteractionEvent Delta="added" EndDate="2010-03-19 16:11:45.355 PDT" Interest="1.0" Kind="attention" Navigation=" " OriginId="org.eclipse.ui.workbench" StartDate="2010-03-19 16:10:44.465 PDT" StructureHandle="none" StructureKind="workingset" />
</InteractionHistory>
This file and others are there as well:
org.eclipse.mylyn.context.core.prefs