I've never heard of AAAA batteries. Okay, I just found them on the Internet, but they aren't usually for sale in drugstores. My opinion: they should have stuck to standard, readily-available batteries.

This is BAD BAD BAD! For less than they're asking ($60) and a smaller size you can get excellent noise blocking in-ear headphones. Cranking up the volume in a noisy environment to drown out the background WILL cause you to lose your hearing. I've spent years on a plane traveling for business and been doing precisely that. As a result I now have a persistent ringing that will never get better, and problems discerning multiple sources of noise - so I can't hear my husband while doing pretty much anything else; as good as that is most of the time in some cases it's kinda annoying.

Chris is absolutely right! I am an Audiologist with two Doctoral Degrees in the field of audiology (research and clinical audiology-the science of hearing) and turning up an ipod to the levels it can maximally go to WITHOUT the Boostaroo will give you a hearing loss! Going louder is just stupid. Once you loose hearing you will wish you had never done such a dumb thing. I played in a band in college and went to many concerts. I pay the price now. Not yet able to wear a hearing aid and not able to hear very well. It STINKS! PRESERVE YOUR HEARING USE INSERT EAR PHONES TO BLOCK THE NOISE AND TURN IT DOWN!

I'll stick to my Shure headphones. They actually do block the noise out without me having to crank the volume all the way up. I can see the crying babies on the subway but I can't hear them. :o)

Just got one and am so glad! I don't listen to music very loudly and hate those huge headphones that block out exterior noise. This is to mainly listen to music ripped from my vinyl and now it sounds much purer and clearer.
Also on long flights, when watching movies on a PSP, you really do need an amplifier as the sound is terribly low.

Revolution Rocks! You obviously haven't listened to a Revolution. It makes your music sound so much better - and it's awesome with DVDs and the PSP.
Plus it images surround sound in my car - so I can plug it into my iPod and FM transmitter.
Of course you don't want to blast the music because it can hurt your hearing. An amp isn't just for loud noise - it gives high end headphones and speakers the power they need - with it you can actually turn down the volume and hear more clearly.
Plus with it - your batteries last 2 - 3 times as long on your player.
For fun, I tried it with my Dad's wireless headphones that he uses with his TV and he said he hears much better. He had trouble hearing the dialoge over the sound effects and music.
I'd like one with a rechargeable battery - but I'm not having trouble finding batteries. Walgreens and Rite Aid both have them.
For my money, this was a deal.