You need to file if you made over $400 from your services.

You should get 1099's from each place you worked for as long as they paid you $600 or more each.

As for not filing if you made less than $5,000, as long as you had federal income tax withheld from your pay, you should file. Otherwise you are giving the government your money. Example, if you made $3,000 and had just $200 withheld... file! You will get the full $200 back. You don't file, you get nothing.