You should be fine, unless you are also building custom commandbars for the Explorer object.
See:
Office Client Developer Content and Resources : Preparing your Existing Solutions to Run on Outlook 2010:
http://blogs.msdn.com/officedevdocs/archive/2009/12/11/preparing-your-existing-solutions-to-run-on-outlook-2010.aspxYou'd need to use Visual Studio 2010 though if you want your add-in to work with 64-bit Outlook 2010.
Eric Legault: MVP (Outlook), MCTS (SharePoint) -- Owner, Collaborative Innovations (http://www.collaborativeinnovations.ca)