Orca has severe performance issues when 'Tabbing' around applications.
The performance is not consistently bad. Some 'Tab' movements are instant while others, especially after multiple 'Tabbing' can block for long periods of time.
Start up any application using the D-Bus AT-SPI module.
Switch to the application.
Press 'Tab' 10-20 times quickly in succession.
The issue seems to be related to the synchronous delivery of Keyboard events, possibly interacting with other calls to the registry daemon or application under examination.
There are some things we could try that may improve this situation. We could attempt to split the registryd up into two separate threads. One dealing with device events and the other dealing with calls to the desktop object.