No doubt you can increase performance of the application by eliminating round-trips and re-querying. I have much experience with this type of application and I have applied this scenario not only with small amount of data but large amount of data. But think twice weather the data should be cached or not because it depend on various things such as application type, data type (how often data is modified) and memory.

Why I used HashTable for this is: it is a dictionary type collection that is optimized for fast retrieval. I do not think that DataSet is really applicable for this operation.

Dinesh