I wonder why people are creating so many crypto currencies and how many of them may sustain? Can anyone here predict what is going to happen? (Not asking to predict what coins are going to sustain as no one would know answer to that).
Many other crypto currencies are inspired by bitcoin, but have a goal that differentiates them from bitcoin. For example, litecoin was design to combat the development of ASICs, so that people with regular computer hardware can mine them. Namecoins provide secure key-value pair storage, and devcoins are somehow used to fund open source endeavors. Others just want to piggy back on the success of bitcoin.
The success and sustainability of these other currencies (often called altcoins) depends on whether or not you can convince others that they are valuable. For example, Namecoins are gaining popularity because you can buy .bit domain names with them.
Many altcoins will likely remain worthless forever, but people will assign a value to some, and those may be sustainable.