I have both Visual Studio 2010 and 2012 installed on the same machine. When I load a project I get the message "Loading toolbar content from package 'Microsoft.VisualStudio.IDE.ToolbarControlsInstaller.ToolbarInstallerPackage' {2C2988B35-07DA-45F1-96A3-BE55D91C8D7A}" in VS 2010's status bar and it just sits there until it's done. To fix this problem I've gone through the registry and removed all instances of the GUID: {2C2988B35-07DA-45F1-96A3-BE55D91C8D7A}. This fixes the loading issue; however, I don't have the Infragistics toolbox with the controls.
Noticed that this issue does not present itself if Visual Studio is running "As Administrator". Today, I opened a solution by double clicking the .sln file and then I opened the same solution with VS that was already running in Administrator mode and it opened no problem while I waited for the other instance to finish loading the toolbox.
Same GUID.