That flash abstraction layer is now built into Arduino, as from 1.0 I think.
Regardless it's only for storing static data at compile time, not for dynamic data at run time. So it's good for reducing RAM usage when for example you have a lot of strings, but no use for saving sensor data etc.
serial communications pre 1.0 IDE
Buffered serial out was introduced in 1.0
What is the buffer size for hardware serial?
I think 64 bytes. Why it was not made variable is anyone's guess and somewhat typical of the (IMO) lack of thought put into some of the Arduino code. Presumably you can edit the appropriate .h file to change it.
Rob