the criteria for an lsac fee waiver is pretty strict i've heard, so don't count your chickens and whatnot.
oh, and to clarify, the OP and i were referring to LSAC's fee waiver for the LSAT and LSDAS. school application fee waivers are a separate issue, though once you qualify for lsac's fee waiver, from what i understand, schools almost always automatically grant application fee waivers. in fact in many cases they are automatically programmed into LSAC's electronic application system (you won't know until you hit checkout which schools have automatically granted you a fee waiver).
also note that you still have to pay the $12 per report requested by schools, but you do get four reports free with the waiver. as noted before, you also get a free copy of superprep.
edit: it might take longer to get processed as the volume of applications increases as we get closer to the test. apply as soon as you can (and register for the test as soon as you can before testing facilities in your area fill up completely).