I have noticed that my brakes are a little weaker than they used to be when I bought the car 3 years ago. The pads are good, but I was wondering if this is the cause of a weaker brake booster or master cylinder?

 

check the main vac line for the brake booster. the one coming off of the engine. and then have your brake fluid flushed and bled. that should help out alot. if youve got the money id suggest upgrading to steel braided lines, to fight brake line bloating.