I've tried many calendar sharing applications to manage the hassle of finding times to meet with people. I finally found one that does not slow down Outlook.
The app I've been using for a few weeks is Tungle. It synchronizes with Outlook without affecing performance of Outlook. What's great is that when you want to meet with multiple people, they can all find times on your schedule that works for them and Tungle automatically selects a time when everyone in the group can make the meeting. So much less hassle than trading emails or having an assistant spend 30 minutes juggling four people's schedules.
Tungle has a "freemium" model, which let's you use it for free or pay a small monthly fee for a branded version. It will also synch mobile with your mobile device.
Please post about any solutions you are using that work or let others know the ones that do NOT work. And, if you try Tungle, please post about how that works for you.