I know you didn't ask about Windows users, but assuming you are from Apple and have an ear there, please forward this message to the appropriate individual...
With my fairly large, multi-gigabyte library, iTunes often takes minutes to respond to user input. Sometimes during syncing it can take up to 30 minutes to respond to my input. Please performance-profile iTunes before frustrated and contractually-obligated-to-use-iTunes iPhone users slap you with a class-action lawsuit.
I haven't experienced this and my library is around 100 GB. Could it be something with your disk? Is the library on a local disk or remote disk? What's the speed (rpm) of the disk?
With my fairly large, multi-gigabyte library, iTunes often takes minutes to respond to user input. Sometimes during syncing it can take up to 30 minutes to respond to my input. Please performance-profile iTunes before frustrated and contractually-obligated-to-use-iTunes iPhone users slap you with a class-action lawsuit.