Since 0.4.6:

Provides printf-style formatting over serial.

printf allows strings to be built by combining a number of values with text.

Serial.printf("Reading temperature sensor at %s...", Time.timeStr().c_str());
float temp = readTemp();
Serial.printf("the temperature today is %f Kelvin", temp);

Running this code prints:

Reading temperature sensor at Thu 01 Oct 2015 12:34...the temperature today is 293.1 Kelvin.

The last printf() call could be changed to printlnf() to avoid a separate call to println().