I did this successfully:
Opened VS2010, choose to create a new Arcmap Add-in project.
Edited the xml by hand to look like this:
<ESRI.Configuration xmlns="http://schemas.esri.com/Desktop/AddIns" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Name>ArcMapAddin1</Name>
<AddInID>{1a65703b-71ec-43e0-901c-d9efbb52da7b}</AddInID>
<Description>Type in a description for this Add-in.</Description>
<Version>1.0</Version>
<Image>Images\ArcMapAddin1.png</Image>
<Author>Kirk</Author>
<Company>AmberGIS</Company>
<Date>4/11/2011</Date>
<Targets>
<Target name="Desktop" version="10.0" />
</Targets>
<AddIn language="CLR" library="ArcMapAddin1.dll" namespace="ArcMapAddin1">
<ArcMap>
<Menus>
<Menu isRootMenu="true" id="MyRootMenu" caption="RootMenu">
<Items>
<Button refID="AmberGIS_ArcMapAddin1_Button1"/>
</Items>
</Menu>
</Menus>
<Commands>
<Button id="AmberGIS_ArcMapAddin1_Button1" class="Button1" message="Add-in command generated by Visual Studio project wizard." caption="My Button" tip="Add-in command tooltip." category="Add-In Controls" image="Images\Button1.png" />
</Commands>
</ArcMap>
</AddIn>
</ESRI.Configuration>
I then ran in debug mode, which brought up arcmap.
Under Customize>Customize Mode, I went to Commands tab and was able to drag and drop RootMenu onto the main menu.

After closing, it was still there.
