Let's see.
In my current project I use already 5 libraries.
My program has quite a lot of different functions, which are triggered by "operational buttons" and a rotary/button setup menu, where the user can modify operational parameters which then will be saved in the EEPROM.
To reduce the number of buttons they have up to 3 different functions (triggered by short, long, double clicking).
The operational functions control two stepper motors, a proximity sensor and 4 LEDs.
So you see, quite a complex sketch and currently I look for squeezing the code such that more SRAM is freed. The best results for that were achieved by using the F-Macro.