Doesn't live up to its billing
Amazon, the packaging, and the Black and Decker website all three lead one to believe that this is designed for powering laptops. The Amazon site can be fairly interpreted to imply that it will power a laptop for 9 hours. Of course this is nonsense that anyone understanding the meaning of 4000mAh will spot immediately. Unfortunately many have been mislead. I knew that I wouldn't get nine hours but I'm not getting anywhere near 4000mAh out of mine either. It works well and is handy but the battery power useable for 120V is closer to 2000mAh. I can't reliably watch an entire DVD on a portable DVD player (no internal battery). The batteries in the pack loose their charge just sitting in storage at a very fast rate. You want to be sure you leave it plugged in until the last possible minute.
For those looking to power their laptop, you'd be better looking to get one of the $250 to $400 lithium based battery packs that is shaped like a laptop. That's what I'm doing now.

Computer power supply
The Black & Decker power supply works great. Just what i needed as I am often without power when working on my computer.

It does not work!
It appears to charge itself, but it will only charge another device for about 5 minutes before dying. I need to return it. Do not recommend.

Very Pleased - Good deal for the price
I bought two of these to extend the taping time for my camcorder. Rather than buy enough batteries specifically for my camcorder (at $56 each)to tape six hours worth of youth football I bought the Black and Decker 100 Watt Power to go. I actually bought two but I havent needed to open the second one because the first has performed so well. I have run a myriad of small items off of it so far and it has performed very well. It does get warm during use so make sure its out where it can breath. My only complaint is that the charge status lights do not give a good representation of when the battery will stop working. It could be still on four or five bars when it quits. It also takes several hours to reach full charge so be patient before you test it out.

Summary - For the low price and versatility I am very pleased with this product.

It came through for a unique situation
I purchased this device to power a low voltage digital music synthesizer for use on a trailer in a local parade. There was no room to use a generator. In tests this power supply was able to power this device for 1.25 hours before the battery level started to drop. The parade last 45 minutes so the power was more than adequate. This will be great to use for practicing where there is no electricity available. I recommend it highly.