* Prices may differ from that shown
We used to use these projectors when I was in university and I have to say that I have had a very mixed experience with them. However, this is probably down to the newness of the technology and the lack of people willing to invest (a portable projector like this is a very small market). I'll give a quick explanation of the product itself, then go into a bit more detail about the different things that it could be used for and also where it would be out of its depth.
This projector doesn't have the same standard video inputs that you would expect to find on a standard projector (VGA, composite, scart...) for one simple reason - they would make the device FAR to big - so this one uses a USB connector - infact - it has two, a standard USB connector and what some people would call a 'printer' connecter (the little square one). It also has what looks like a headphone jack that can accept a video input. It also (amazingly) has a small built in speaker that can play sound, although dont expect much from this - it is a projector that costs less than £150!
In terms of operation, it is fairly easy, plug it into the wall and then plug a USB into your computer. I've tried this on a number of operating systems, details are below on my success
WINDOWS 7 - Works out the box, drivers are found by OS
VISTA - Works out the box, drivers found by OS
XP - You will need to tell it where the drivers are (either on the disk or online)
I was pleasantly surprised with the image quality, the projector manages to pump out a nice 1280x800 resolution, which is about the same as most standard laptops nowadays - note, this resolution is somewhere just above 720p but WAY below 1080p if you are wanting to watch movies. The only downside with the image quality (predictably) is that is really isn't bright at all - the lens can only manage 70 lumens (standard projectors are around the 2000+ mark).
So with this type of projector, its really good for keeping next to your laptop if you ever want to show holiday snaps to a lot of people at once, just make sure that you are able to turn the lighting in the room down a little bit. Its also good if want to set up projector to game on (nothing beats a bit of left for dead in the dark on a big screen!). Situations that it wouldn't be any use are generally where the lighting is quite high (outdoors, well lit rooms etc), you wont be able to see anything at all.
Overall, this is a really good projector if you can find a use for it. The low price point helps a lot in trying to sell it but it really is one of these things that you're only going to get if you have a lot of disposable income but dont want to invest in a standard projector.