You can use the Developer Dashboard in SharePoint 2010—even if you’re not a developer. Like many Microsoft naming conventions, this feature has a misleading moniker. It’s for devs, but also for IT pros.
With Developer Dashboard, you can see time to load and render various page components, database query info, Web Part processing time, and any critical events or alerts. It's good for diagnosing problem Web Parts on a page or long load list time.
Property values are off, on, and on-demand, which lets you can toggle switch it per page. It's something you'll want to use judiciously, but it can help you break down a page and see what's going on with it. To enable it, go to STSADM.
“Why SharePoint 2010 Developer Dashboard Is For All IT Professionals” or Bill Baer’s blog post, "Welcome to the Developer Dashboard." I saw it in action on Shane Young's TechNet demo, which I now cannot find. But the guys above have enough info to get you interested.