Hello! I'm a regular user of Photo Stream, and may be able to help you get some value out of it.
Firstly, Photo Stream isn't designed to be a permanent store of all your photos. If you're looking for a permanent store of your photos on the internet cloud storage options such as Dropbox or Photobucket are the way to go.
Photo Stream main job is to automatically push your photos from device to device, so they can be viewed on any other Apple device in your house.
The most common example would be taking a photo with an iPhone, then being able to look at the photo seconds later on an iPad. If you have other Apple devices in the house such as an Apple TV connected to your television or Mac computer, the same photo will automatically pop up on these devices after a couple of seconds as well.
The storage is temporary, so each photo will only stay in photo stream for 30 days before being automatically deleted to allow new photos to enter the stream. However you can also manually delete the photos if you want to remove them from the stream earlier.
The great thing is that the devices don't have to be in the same house. The most the best value our house gets out of photo stream is taking photos and then creating a Photo Stream album that we share with grandparents and other relatives in Australia.
These albums then automatically pop up on the iPads in Australia without the grandparents having to request them or log into a photo sharing website. So it ends up being a really easy way of creating a digital photo album to share photos internationally.
So it's two different things really. If you want to store photos permanently on the Internet, then Photo Stream is not you. However if you want a really simple way of pushing your photos around different Apple devices in your house or to your relatives, it's a really quick and easy solution.