Online web part gallery and performance
If you are not already aware, the Online Web Part Gallery (one of the choices when you browse for new web parts) is a huge performance hit. On a system that I am currently working on, the Browse selection page would take almost 30 seconds to come up with the gallery enabled. When I deactivated the gallery, it took less than 2!
To turn off the Online web part gallery, start the SharePoint Central Administration page, select “configure virtual server settings”, select your virtual server, select “Manage security settings for Web Part Pages” and then select “Disable” under the Online Web Part Gallery section.