There are just so many apps available for taking pictures on the iPhone that one does not easily know what to choose, althoug a little googling will give you equally lots of lists with peoples' favourites. Hipstamatic is sure to turn up as one of them. So I donwloaded it a whle ago, but I must admit that I have not really often found a good way for using it.
It is a nice toy, but you really have to take a different look at taking pictures. I find that difficult. My vision is more 'traditional', most of the time. I want to take pictures that are sharp (selectively), well-exposed (for the purpose), etc. The creativity is in finding a good perspective, a good compisition--and in knowing what the picture should get across to the viewers.