No data on SD Card, Data logging shield

[adafruit_support_mike]

You want the same timing logic used here: http://arduino.cc/en/Tutorial/BlinkWithoutDelay

The basic idea is that you call 'millis()' to keep track of time. Store a timestamp every time you write to the logfile, and keep comparing that to the current time on every pass through the main loop. If it's been more than two seconds since the last write, do a new write and update the timestamp.